Heilongjiang is in the __________of China.

　　One summer day a raindrop (雨滴) fell from a cloud. Many other raindrops fell at the same time, but our story is about just one raindrop.

　　The raindrop fell to the ground on the side of a hill. The water in the raindrop ran down the hill into a little river. The little river carried the raindrop to a big river. Then the raindrop travelled far to the east into the sea. There the water of the raindrop mixed itself with the salt water of the sea.

　　Now the water of the raindrop was on the surface (表面)of the sea. As the sun　　made it very warm, it changed into steam (蒸气).

　　The steam left the sea and went up into the air, and it did not carry any salt with it. It had left the salt in the sea.

　　The steam from the raindrop moved with the warm air towards the north. On the way the warm air met some cold air. The cold air pushed (推) the warm air high above the ground. The warm air became cool when it went up, and the steam in it changed into very small drops of water again. There were millions and millions of these small drops in the cloud. The small drops came together into bigger and bigger drops. Our raindrop was one of them. Now the drop became so big that it was too heavy to stay in the .cloud, and it fell to the ground. In this way the water of our raindrop, started travelling to the sea again.

1．This story is about ________ .

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2．When the raindrop travelled into ________ , the water in it became ________ .

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3．The water of the raindrop went up into the air from the sea ________ salt ________ it changed into steam.

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4．The steam changed ________ into very small drops of water ________ it met some cold air.

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5．The small water drops in the cloud fell down because ________ .

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A．there were millions and millions of them in the cloud

B．the sea wanted to take them back

C．they wanted to start travelling on the ground again

D．they became so heavy that the cloud couldn't hold them up any longer