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We know a lot about our world. When people are near a river or a sea, you feel cool. Why did the sun make the earth hot, but it can't make the water hot. Though the air over the earth becomes hot, the air over the water stays cool. The hot air over the earth goes up, then the cool air over the water moves in and takes the place of the hot air. When you are near a river or a sea, you feel the cool air when it moves in. You feel the wind and the wind makes you cool.

However, scientists can't answer all of the questions. If we ask "Why is the sea full of salt(盐)?" scientists will say that the salt comes from rocks. When a rock gets very hot or very cool, it cracks(破裂）, and rain falls into the cracks. The rain then carries the salt into the earth and the rivers. The rivers carry the salt into the sea. But then we ask "Why do not the seas get saltier?" scientists are not sure about the answer to the question. Scientists can explain many things, but not everything.

1.Why do you feel cool when you are near the sea?

A Because the beach is hot.

B Because the sea water is cold.

C Because the water is colder than the land.

D Because cool air from the water moves towards the land.

解析：选D。D 细节理解题。根据第一段第五句The hot air over the earth goes up, then the cool air over the water moves in and takes the place of the hot air.可知大地上的热气上升，然后水上的冷空气向陆地移动，代替热气的位置，故选D。

2.Where does the salt in the sea come from?

A Air.

B Rain.

C Rocks.

D Rivers and lakes.

解析：选C。C 细节理解题。根据第二段第二句If we ask “Why is the sea full of salt?” scientists will say that the salt comes from rocks.可知海洋的盐来自岩石，故选C。

3.When does a rock crack?

A When rain falls.

B When it gets very hot.

C When it gets very cold.

D Both B and C.

解析：选D。D 细节理解题。根据第二段第三句When a rock gets very hot or very cool, it cracks, and rain falls into the cracks.可知当岩石变热或变冷时，它会开裂，雨落在裂缝里，故选D。

4.What do scientists know?

A Nothing about the sea.

B Everything about the sea.

C Why the sea gets saltier.

D What makes people cool near the sea.

解析：选D。D 细节理解题。根据全文可知科学家可以解释为什么海边比较凉爽，故选D。

5.What is the main idea of this passage?

A Scientists can explain everything.

B The salt in the sea comes from rocks.

C People feel cold when they are near a lake or a sea.

D Scientists can explain many things, but not everything.

解析：选D。D 细节理解题。根据全文并结合第二段最后一句Scientists can explain many things, but not everything.可知科学家可以解释很多事情，但不能解释一切，故选D。