Weather changes when the temperature and the amount of water in the atmosphere changes. 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 vapor in clouds condenses(凝结). Drops of water form and fall to the ground. The water soaks into the ground and feeds steams 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 vapor. The vapor rises onto the air. Water vapor

is normally invisible. On a very damp or humid day, however, you can sometimes see water vapor rising from a puddle(水坑) or pond in a mist(薄雾)above the water. Water vapor also gets into the air from living things. Trees and other plants take in water through their roots and give off water vapor from their leaves. People and land animals drink water and breathe out water vapor. 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 continues even if snow or hail(冰雹) fall instead because both eventually melt to form water. The amount of water vapor in the air depends on the temperature. The air is more moist(潮湿)in the tropics(热带) than in the cold polar regions.

1. What is the main idea of the passage?  

A. Water cycle      

B. Water vapor  

C. How rain forms  

D. Water ,vapor, rain

2. How many ways of the water returning to the air are discussed in the text?  

A. Two  

B. Three  

C. Four    

D. Five

3. Whether water vapor 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

4. From the passage we get to know___________.

A. there is more water vapor in the air in the tropics than in cold polar regions

B. there is more water vapor 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 vapor in the air depends on how often it rains