Suppose you have a brick and a sponge which are exactly the same size. The brick and the sponge will occupy the same amount of space, but they will not weigh the same. If two things are exactly the same size, but differ in weight, then they have different densities. The one with the greater weight for the same size has the greater density. The one with lower weight for the same size has the lower density.
Now apply this idea to fluids. You know that water and air expand when they are heated and therefore become less dense. If you poured a cupful of very hot water and let it cool, you would have a little less than a cupfull of cool water. If you weighed a cupful of very hot water and a cupful of cool water, the cupful of very hot water would weigh a little less.
The cupful of cool water, being a little heavier than the cupful of hot water, would really have a little more water in it. Cold water is denser than hot water. Likewise, cold air is denser than hot. air. The greater weigh! of !he denser material makes it fall to the bottom of the container. It pushes up the less dense material.
Two things are the same size but differently weight. That means______.

A:the heavier one has lower density B:the lighter one has greater density C:they have the same density D:they have different density

When aluminum was first produced about a hundred and fifty years ago, it was so difficult to separate from the ores in which it was found that its price was higher than that of gold. The price remained high until a new process was discovered for refining the metal with the aid of electricity approximately three quarters of a century later. The new method was so much cheaper that aluminum became practical for many purposes, one of which was making pots and pans.
Aluminum is lightweight, rustproof and easily shaped into different forms. By mixing it with other metals, scientists have been able to produce a variety of alloys, some of which have the strength of steel but weigh only one third as much.
Today, the uses of aluminum are innumerable. Perhaps its most important use is in transportation. Aluminum is found in the engine of automobiles, in the hulls of boats. It is also used in many parts of airplanes. In fact, the huge "airbus" planes would probably never have been produced if aluminum did not exist. By making vehicles lighter in weight aluminum has greatly reduced the amount of fuel needed to move them. Aluminum is also being used extensively in the building industry in some countries.
Since aluminum is such a versatile(多用的) metal, it is fortunate that bauxite(铝土矿), which is one of its chief sources, is also one of the earth’s most plentiful substances. As the source of aluminum is almost inexhaustible, we can expect that more and more uses will be found for this versatile metal.

Aluminum is （）

A:lightweight, rustproof but not easily shaped into different forms B:heavyweight, rustproof and easily shaped into different forms C:lightweight, rustproof and easily shaped into different forms D:lightweight and easily shaped into different forms but it is easy to become rusty

(There) are (thousand) of (different) types (of) roses.

A:There B:thousand C:different D:of

Directions: There are five reading passages in this part. Each passage is followed by four questions. For each question there are four suggested answers marked A, B, C and D. Choose one best answer and blacken the corresponding letter on the Answer Sheet.
Passage One

Two things are the same size but differently weight. That means______.

A:the heavier one has lower density B:the lighter one has greater density C:they have the same density D:they have different density

Scientists have found a way to use hair to figure out where a person is from and where that person has been. The finding could help solve crimes, among other useful applications.
Water is central to the new technique. Our bodies break water down into its parts: hydrogen and oxygen. Atoms of these two elements end up in our tissues and hair.
But not all water is the same. Hydrogen and oxygen atoms can vary in how much they weigh. Different forms of a single element are called isotopes. And depending on where you live, tap water contains unique proportions of the heavier and lighter isotopes of hydrogen and oxygen.
Might hair record these watery quirks That’s what James R. Ehleringer, an environmental scientist at the University of Utah in Salt Lake City, wondered to find out he and his colleagues collected hair from barbers and hair stylists in 65 cities in 18 states across the United States. The researchers assumed that the hair they collected came from people who lived in the area.
Even though people drink a lot of bottled water these days, the scientists found that hair overwhelmingly reflected the concentrations of hydrogen and oxygen isotopes in local tap water. That’s probably because people usually cook their food in the local water. What’s more, most of the other liquids people drink including milk and soft drinks contain large amounts of water that also come from sources within their region.
Scientists already knew how the composition of water varies throughout the country. Ehlernger and colleagues combined that information with their results to predict the composition of hair in people from different regions. One hair sample used in Ehleringer’s study came from a man who had recently moved from Beijing, China, to Salt Lake City. As his hair grew, it reflected his change in location.
The new technique can’t point to exactly where a person is from, because similar types of water appear in different regions that span a broad area but authorities can now use the information to analyze hair samples from criminals or crime victims and narrow their search for clues.
What does the last paragraph tell you

A:The new technique can tell precisely where a person lives. B:Water supplied in different regions all come from the same source. C:Types of water used in different regions provide useful information for the police. D:Hair samples provide the most important clues to identify crimes.

Costs associated with countries such as( )or a different culture may make international trade more costly than domestic trade．

A:different nature factors B:political difference C:different legal system D:different language