Although many factors affect human health during periods in space, weightlessness is the dominant and single most important one. The direct and indirect effects of weightlessness lead to a series of related responses. Ultimately, the whole body, from bones to brain, kidneys to bowels, reacts.
When space travelers grasp the wall of their spacecraft and jerk their bodies back and forth, they say it feels as though they are stationary and the spacecraft is moving. The reason is based in our reliance on gravity to perceive our surroundings.
The continuous and universal nature of gravity removes it from our daily notice, but our bodies never forget. Whether we realize it or not, we have evolved a large number of silent, automatic reactions to cope with the constant stress of living in a downward-pulling world. Only when we decrease or increase the effective force of gravity on our bodies do our minds perceive it.
Our senses provide accurate information about the location of our center of mass and the relative positions of our body parts. Our brains integrate signals from our eyes and ears with other information from the organs in our inner ear, from our muscles and joints, and from our senses of touch and pressure.
The apparatus of the inner ear is partitioned into two distinct components: circular, fluid-filled tubes that sense the angle of the head, and two bags filled with calcium crystals embedded in a thick fluid, which respond to linear movement. The movement of the calcium crystals sends a signal to the brain to tell us the direction of gravity. This is not the only cue the brain receives. Nerves in the muscles, joints, and skin—particularly the slain on the bottom of the feet—respond to the weight of limb segments and other body parts.
Removing gravity transforms these signals. The inner ear no longer perceives a downward tendency when the head moves. The limbs no longer have weight, so muscles are no longer required to contract and relax in the usual way to maintain posture and bring about movement. Nerves that respond to touch and pressure in the feet and ankles no longer signal the direction of down. These and other changes contribute to orientation illusions, such as a feeling that the body or the spacecraft spontaneously changes direction. In 1961 a Russian astronaut reported vivid sensations of being upside down; one space shuttle specialist in astronomy said, "When the main engines cut off, I immediately felt as though we had inverted 180 degrees." Such illusions can recur even after some time in space.
"Whether we realize it or not" (Line 2, Par

A:A．3), "it" refers ______. weightlessness the continuous and universal nature of gravity the fact that our bodies never forget the previous statements

Is it possible that the ideas we have today about ownership and property rights have been so universal in the human mind that it is truly as if they had sprung from the mind of God By no means. The idea of owning and property emerged in the mists of unrecorded history. The ancient Jews, for one, had a very different outlook on property and ownership, viewing it as something much more temporary and tentative than we do. 　　The ideas we have in America about the private ownership of productive property as a natural and universal right of mankind, perhaps of divine origin, are by no means universal and must be viewed as an invention of man rather than a decree (order) of God. Of course, we are completely trained to accept the idea of ownership of the earth and its products, raw and transformed. It seems not at all strange; in fact, it is quite difficult to imagine a society without such arrangements. If someone, some individual, didn’’t own that plot of land, that house, that factory, that machine, that tower of wheat, how would we function What would the rules be Whom would we buy from and how would we sell 　　It is important to acknowledge a significant difference between achieving ownership simply by taking or claiming property and owning what we tend to call the "fruit of labor". If I, alone or together with my family, work on the land and raise crops, or if I make something useful out of natural material, it seems reasonable and fair to claim that the crops or the objects belong to me or my family, are my property, at least in the sense that I have first claim on them. Hardly anyone would dispute that. In fact, some of the early radical workingmen’’s movements made (an ownership) claim on those very grounds. As industrial organization became more complex, however, such issues became vastly more intricate, It must be clear that in modern society the social heritage of knowledge and technology and the social organization of manufacture and exchange account for far more of the productivity of industry and the value of what is produced than can be accounted for by the labor of any number of individuals. Hardly any person can now point and say, "That--that right there--is the fruit of my labor. "We can say, as a society, as a nation--as a world, really--that what is produced is the fruit of our labor, the product of the whole society as a collectivity. 　　We have to recognize that the right of private individual ownership of property is man-made and constantly dependent on the extent to which those without property believe that the owner can make his claim stick. We learn by inference that private property may

A:be viewed as a design of inventive powers. B:be treated as a discovery of our ancestors. C:serve as the universal rule of transactions. D:function as the basis of market economy.

Is it possible that the ideas we have today about ownership and property rights have been so universal in the human mind that it is truly as if they had sprung from the mind of God By no means. The idea of owning and property emerged in the mists of unrecorded history. The ancient Jews, for one, had a very different outlook on property and ownership, viewing it as something much more temporary and tentative than we do. 　　The ideas we have in America about the private ownership of productive property as a natural and universal right of mankind, perhaps of divine origin, are by no means universal and must be viewed as an invention of man rather than a decree (order) of God. Of course, we are completely trained to accept the idea of ownership of the earth and its products, raw and transformed. It seems not at all strange; in fact, it is quite difficult to imagine a society without such arrangements. If someone, some individual, didn’’t own that plot of land, that house, that factory, that machine, that tower of wheat, how would we function What would the rules be Whom would we buy from and how would we sell 　　It is important to acknowledge a significant difference between achieving ownership simply by taking or claiming property and owning what we tend to call the "fruit of labor". If I, alone or together with my family, work on the land and raise crops, or if I make something useful out of natural material, it seems reasonable and fair to claim that the crops or the objects belong to me or my family, are my property, at least in the sense that I have first claim on them. Hardly anyone would dispute that. In fact, some of the early radical workingmen’’s movements made (an ownership) claim on those very grounds. As industrial organization became more complex, however, such issues became vastly more intricate, It must be clear that in modern society the social heritage of knowledge and technology and the social organization of manufacture and exchange account for far more of the productivity of industry and the value of what is produced than can be accounted for by the labor of any number of individuals. Hardly any person can now point and say, "That--that right there--is the fruit of my labor. "We can say, as a society, as a nation--as a world, really--that what is produced is the fruit of our labor, the product of the whole society as a collectivity. 　　We have to recognize that the right of private individual ownership of property is man-made and constantly dependent on the extent to which those without property believe that the owner can make his claim stick. We learn by inference that private property may

A:be viewed as a design of inventive powers. B:be treated as a discovery of our ancestors. C:serve as the universal rule of transactions. D:function as the basis of market economy.

Is it possible that the ideas we have today about ownership and property rights have been so universal in the human mind that it is truly as if they had sprung from the mind of God By no means. The idea of owning and property emerged in the mists of unrecorded history. The ancient Jews, for one, had a very different outlook on property and ownership, viewing it as something much more temporary and tentative than we do. 　　The ideas we have in America about the private ownership of productive property as a natural and universal right of mankind, perhaps of divine origin, are by no means universal and must be viewed as an invention of man rather than a decree (order) of God. Of course, we are completely trained to accept the idea of ownership of the earth and its products, raw and transformed. It seems not at all strange; in fact, it is quite difficult to imagine a society without such arrangements. If someone, some individual, didn’’t own that plot of land, that house, that factory, that machine, that tower of wheat, how would we function What would the rules be Whom would we buy from and how would we sell 　　It is important to acknowledge a significant difference between achieving ownership simply by taking or claiming property and owning what we tend to call the "fruit of labor". If I, alone or together with my family, work on the land and raise crops, or if I make something useful out of natural material, it seems reasonable and fair to claim that the crops or the objects belong to me or my family, are my property, at least in the sense that I have first claim on them. Hardly anyone would dispute that. In fact, some of the early radical workingmen’’s movements made (an ownership) claim on those very grounds. As industrial organization became more complex, however, such issues became vastly more intricate, It must be clear that in modern society the social heritage of knowledge and technology and the social organization of manufacture and exchange account for far more of the productivity of industry and the value of what is produced than can be accounted for by the labor of any number of individuals. Hardly any person can now point and say, "That--that right there--is the fruit of my labor. "We can say, as a society, as a nation--as a world, really--that what is produced is the fruit of our labor, the product of the whole society as a collectivity. 　　We have to recognize that the right of private individual ownership of property is man-made and constantly dependent on the extent to which those without property believe that the owner can make his claim stick. We learn by inference that private property may

A:be viewed as a design of inventive powers. B:be treated as a discovery of our ancestors. C:serve as the universal rule of transactions. D:function as the basis of market economy.

Science is committed to the universal.

The Turing machine is an abstract (71) of computer execution and storage introduced in 1936 by Alan Turing to give a mathematically precise definition of (72) . or ’mechanical procedure’. As such it is still widely used in theoretical computer science, especially in (73) theory and the theory of computation. The thesis that states that Turing machines indeed capture the informal notion of effective or mechanical method in logic and mathematics is known as Turing’s thesis.
Every Turing machine computes a certain (74) partial function over the strings over its alphabet. In that sense it behaves like a computer with a fixed program. However, as Alan luring already described, we can encode the action table of every Turing machine in a string. Thus we might try to construct a Turing machine that expects on its tape a string describing an action table followed by a string describing the input tape, and then computes the tape that the encoded Turing machine would have computed. As Turing showed, such a luring machine is indeed possible and since it is able to simulate any other Turing machine it is called a (75) Turing machine.
A universal Turing machine is Turing complete. It can calculate any recursive function, decide any recursive language, and accept any recursively enumerable language. According to the Church-Turing thesis, the problems solvable by a universal Turing machine are exactly those problems solvable by an algorithm or an effective method of computation, for any reasonable definition of those terms.

A:universal B:special C:complete D:changeable