Centuries ago, man discovered that removing moisture from food helps to preserve it, and that the easiest way to do this is to expose the food to sun and wind. In this way the North American Indians produce pemmican, the Scandinavians make stockfish and the Arabs dry dates and apricot leather.
All foods contain water-cabbage and other leaf vegetables contain as much as 93% water, potatoes and other root vegetables 80%, lean meat 75% and fish anything from 80% to 60% depending on how fatty it is. If this water is removed, the activity of the bacteria that cause food to deteriorate is checked.
Fruit is sun-dried in Asia Minor, Greece, Spain and other Mediterranean countries, and also in California, South Africa and Australia. The methods used vary, but in general, the fruit is spread out on trays in drying yards in the hot sun. In order to prevent darkening, pears, peaches and apricots are exposed to the fumes of burning sulfur before drying. Plums, for making prunes, and certain varieties of grapes for making raisins and currants, are dipped in an alkaline solution in order to crack the skins of the fruit slightly and remove their wax coating, so increasing the rate of drying.
Nowadays most foods are dried mechanically. The conventional method of such dehydration is to put food in chambers through which hot air is blown at temperatures of about 110℃ at entry to about 43℃ at exit. This is the usual method for drying such things as vegetables, minced meat, and fish.
Liquids such as milk, coffee, tea, soups and eggs may be dried by pouring them over a heated horizontal steel cylinder or by spraying them into a chamber through which a current of hot air passes. In the first case, the dried material is scraped off the roller as a thin film which is then broken up into small, though still relatively coarse flakes;" in the second process it falls to the bottom of the chamber as a fine powder. Where recognizable pieces of meat and vegetables are required, as in soup, the ingredients are dried separately and then mixed.
Dried foods take up less room and weigh less than the same food packed in cans or frozen, and they do not need to be stored in special conditions. For these reasons they are invaluable to climbers, explorers and soldiers in battle, who have little storage space. They are also popular with housewives because it takes so little time to cook them. Usually it is just a case of replacing the dried-out moisture with boiling water.
Housewives like dried foods because ______.

A:they arc quick to prepare B:they weigh less than the same canned foods C:they are much better than the frozen foods D:they can be replaced by moisture with boiling water

Text 2

Housewives like dried foods because ______.

A:they arc quick to prepare B:they weigh less than the same canned foods C:they are much better than the frozen foods D:they can be replaced by moisture with boiling water

When the temperature of a liquid is raised enough, the liquid boils. This means that bubbles of vapor, containing millions of molecules, form below the surface. In order for such bubbles to be produced, the pressure of the vapor inside them must be equal to the pressure of the air upon the surface of the liquid. If the air pressure is greater, the bubble will collapse. The boiling point of a liquid, then, is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure upon the liquid at the surface.
The pressure of the atmosphere at sea level is about one kilogram per square centimeter. We call this pressure one atmosphere. The boiling point of a liquid, therefore, is the temperature at which its vapor pressure equals one atmosphere. The boiling point of water is 100 Celsius; of ethyl alcohol 78.5 Celsius; of mercury, 356.9 Celsius.
If the pressure on the surface of the water is reduced, the boiling point will be lower. Now the higher up we go from sea level, the lower the atmospheric pressure becomes, since there is less air to press upon us. Hence, while water boils at sea level at a temperature of 100 Celsius, its boiling point on a mountain three kilometers high is only 90 Celsius. Since the temperature of water does not rise as a result of boiling, it would take you longer to cook potatoes or carrots in boiling water on the mountain than it would at sea level.

Which statement of the following is correct according to this passage（）

A:The boiling point of a liquid is the original temperature. B:The higher the pressure on the surface of the liquid, the quicker the boiling point will be reached. C:The boiling point of a liquid is 100 Celsius. D:Both Ｂ and Ｃ.

When the temperature of a liquid is raised enough, the liquid boils. This means that bubbles of vapor, containing millions of molecules, form below the surface. In order for such bubbles to be produced, the pressure of the vapor inside them must be equal to the pressure of the air upon the surface of the liquid. If the air pressure is greater, the bubble will collapse. The boiling point of a liquid, then, is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure upon the liquid at the surface.
The pressure of the atmosphere at sea level is about one kilogram per square centimeter. We call this pressure one atmosphere. The boiling point of a liquid, therefore, is the temperature at which its vapor pressure equals one atmosphere. The boiling point of water is 100 Celsius; of ethyl alcohol 78.5 Celsius; of mercury, 356.9 Celsius.
If the pressure on the surface of the water is reduced, the boiling point will be lower. Now the higher up we go from sea level, the lower the atmospheric pressure becomes, since there is less air to press upon us. Hence, while water boils at sea level at a temperature of 100 Celsius, its boiling point on a mountain three kilometers high is only 90 Celsius. Since the temperature of water does not rise as a result of boiling, it would take you longer to cook potatoes or carrots in boiling water on the mountain than it would at sea level.

Which statement of the following is false according to the passage（）

A:The boiling point of water on a mountain three kilometers high is only 90 Celsius. B:It would take you longer to cook potatoes in boiling water on the mountain than it would at sea level. C:When the temperature of a liquid is raised enough, the liquid boils. D:The boiling point of water on a mountain six kilometers high is 95 Celsius.

When the temperature of a liquid is raised enough, the liquid boils. This means that bubbles of vapor, containing millions of molecules, form below the surface. In order for such bubbles to be produced, the pressure of the vapor inside them must be equal to the pressure of the air upon the surface of the liquid. If the air pressure is greater, the bubble will collapse. The boiling point of a liquid, then, is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure upon the liquid at the surface.
The pressure of the atmosphere at sea level is about one kilogram per square centimeter. We call this pressure one atmosphere. The boiling point of a liquid, therefore, is the temperature at which its vapor pressure equals one atmosphere. The boiling point of water is 100 Celsius; of ethyl alcohol 78.5 Celsius; of mercury, 356.9 Celsius.
If the pressure on the surface of the water is reduced, the boiling point will be lower. Now the higher up we go from sea level, the lower the atmospheric pressure becomes, since there is less air to press upon us. Hence, while water boils at sea level at a temperature of 100 Celsius, its boiling point on a mountain three kilometers high is only 90 Celsius. Since the temperature of water does not rise as a result of boiling, it would take you longer to cook potatoes or carrots in boiling water on the mountain than it would at sea level.

Which one is the best title for the passage（）

A:Boiling Point of Liquids. B:Three States of Water. C:What Is One Atmosphere. D:Temperature of Liquids.

A group of scientists rowing toward the center of a lake saw something shocking. They turned back as fast as they could. What had they seen. The lake was boiling!
The group was investigating a crater lake in the mountains of St. Vincent. A crater lake is the mouth of a volcano that has been dormant for some time and has filled with water.
This particular crater was the tip of a volcano called Soufriere, which erupted last in 1902. Since that time, it had not shown any signs of action. But in the fall of 1971, mountain climbers who had hiked near the lake returned to the lowlands with strange stories. They said the water had turned yellow and was giving off a smell like burnt eggs. A seething fog was rising from the lake’s surface.
Local scientists rushed to Soufriere to see if this might be the beginning of a new volcanic explosion. They found a huge black mass in the middle of the water. It was a great blob 1,000 feet long and 300 feet wide. Lava had pushed up through the bottom of the lake and formed a new island.
The investigators wanted to make sure that the volcano was safe, and that the lava would not over- flow into the surrounding countryside. But they could never reach the island to study it, because the lava was so hot that the water around it bubbled and boiled.

This passage is about （　）

A:mountain climbing B:a boiling lake C:a new volcanic island D:a mysterious blob

There are thousands of volcanoes (火山) all over the world. What makes volcanoes What happens
The inside of the earth is very hot. Because it is very, very hot, the rock has melted like ice. It has become liquid, like water. It is always boiling, like water in a kettle. If you have seen a kettle boiling, you know that the steam and boiling water try to get out. The very hot melted rock inside the earth also tries to get out. Usually it cannot because the outside of the earth is too thick and strong.
But in some places the outside of the earth is thin and weak. Sometimes a crack appears. The hot melted rock, which we call "lava" (熔岩), pushes out through the crack and bursts through. Steam and gas shoot up into the air and the hot melted lava pours out. Big pieces of rock may be thrown high into the air.
After a while the volcano becomes quiet again. The melted lava becomes hard. Later the same thing happens again and again. Each time more hot lava pours out on top of the cold lava and then becomes hard. In this way a kind of mountain is built up, with a hole down the middle. Perhaps the volcano will then be quiet. Perhaps it will start again hundreds of years later.
Vesuvius is the name of a very famous volcano in Italy. It first came to life many, many years ago. It was quiet for hundreds of years. Then in the year 79 it suddenly burst. A great cloud of smoke shot up into the sky with great burning rocks. Hot lava poured down its sides. About 3,000 people were killed.
This has happened again many times since that year. Sometimes no damage was caused, or only little damage. But there was serious damage in the years 472, 1631, 1794, 1861, 1872 and 1906. You can see that a volcano can stay alive for many years. There was also serious damage in 1914 but there has not been any since that year.

According to the passage, a volcano sends out （　）.

A:boiling water B:boiled water C:melted rock D:melted ice