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 vapor in clouds condenses (凝结). 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 vapor. The vapor rises onto the air. Water vapor is normally invisible. On a very damp of 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 t
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 region because there are fewer vapors
D. the amount of water vapor in the air depends on how often it rains
关于腹膜后恶性淋巴瘤的叙述，正确的是（）
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