人体感染肺吸虫有可能是因为（） A.喝溪水，吃溪蟹、淡水鱼 B.吃淡水虾、荸荠，喝生

关于液压系统平压阀零部件的更换，拆卸之前，应（）。

A、做好必要的标记和标识

B、拆卸固定螺栓

C、拆卸损坏的溢流阀和减压阀，并做好连接油管防护

D、关闭电源

多项式3x²y-2xy+4x-1是______次多项式，常数项是______．

以下角膜移植排斥反应可能性最大的是（）

A.角膜白斑

B.圆锥角膜

C.Fuchs内皮营养不良

D.大泡性角膜病变

E.角膜化学伤

手阳明大肠经人（）

A．耳

B．目

C．上齿

D．下齿

阅读理解。

        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(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 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(水坑) or pond in a mist(薄雾) 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 continues even if snow or hail(冰雹) fall instead because

both eventually melt to form water. The amount of water vapour 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 vapour.

C. How rain forms.     

D. Water, vapour, 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 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

4. From the passage we get to know _______.  

A. there is more water vapour in the air in the 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 vapour  

D. the amount of water vapour in the air depends on how often it rains