C【节选】
Weather changes when the temperature and the amount of water in the atmosphere change. We can see and feel water coming from the atmosphere when we have rain. But the water must somehow get back to the atmosphere. Meteorologists call this the water cycle.
There are many stages in the water cycle. Rain falls when water vapour in clouds condenses(冷却成液体). Drops of water form and fall to the ground. The water soaks into the ground and feeds streams and rivers. A lot of rain falls into the sea. The heat of the sun evaporates some of the water in the ground and in the rivers, lakes and the sea. It changes the liquid water into water vapour. The vapour rises onto the air. Water vapour is normally invisible. On a very damp or humid day, however, you can sometimes see water vapour rising from a puddle or pond in a mist above the water. Water vapour also gets into the air from living things. Trees and other plants take in water through their roots and give off water vapour from their leaves. People and land animals drink water and breathe out water vapour. In all these ways the water returns to the air. There it gathers to form clouds and condenses to form rain. The rain falls to earth, and the cycle starts again. It contains even if snow or hail fall instead because both eventually melt and form water. The amount of water vapour is more in the air tropics than in the cold polar regions.
( ) 48. What is the main idea of the passage?
A. Water cycle. B. Water vapour.
C. How rain forms. D. Water, vapour, rain.
( ) 49. How many ways of the water returning to the air are discussed in the text?
A. Three B. Four C. Five D. Six
( ) 50. Whether water vapour can be seen or not depends on_____.
A. how much water is evaporated
B. how good your eyes are
C. in which way water is evaporated
D. climate or weather
( ) 51. From the passage, we get to know_____.
A. there is more water vapour in the air tropics than in cold polar regions
B. there is more water vapour in the air in cold polar region than in the tropics
C. it gets more rain in the tropics than in cold polar regions because there is less vapor
D. the amount of water vapour in the air depends on how often it rains
(选摘原因：内容上属于自然科学类，但又与生活常识息息相关，题目也难易兼有，比较能考察学生对语篇的分析和判断能力。)
