Question

Have you ever noticed when your sweat dries it will leave marks on your T-shirt? The marks are tiny bits of salt. If you go to the seaside, you will know that seawater does the same to your clothes, because it also has a lot of salt in it.

Water evaporates from the surface of the sea but the salt remains. Have you ever thought about whether the seas will keep getting saltier? The answer is no. The oceans have stayed at about 3.5 percent salt content for hundreds of millions of years. It keeps a constant level of salt in different ways.

Pick up a seashell and weigh it in your hand. It is heavy. All animals need sodium to live and most need calcium to build bone an shells. The seashell, like all sea animals, gets its sodium and calcium from seawater. When animals die, their salt is locked up in bins and shells, which drop to the bottom of the sea.

Seawater and rocks react with each other not just in one way. Sea salt not only reacts with rocks, but also reacts with the rocks of the ocean crust (壳) and volcanic lava. The reactions take some of the salt in seawater away from the sea.

The outer hard crust of the earth is made up of about a dozen hard plates that drift on very hot, soft rock like floating islands on a sea. The heat within the earth is not the same everywhere and the plates move because of the heat. When an ocean plate knocks into a land plate, the thinner land plate floats over the ocean one. The ocean floor gets pushed under and its salty rocks, shells and bones, are lost deep within Earth.

So, that’s why the seas are salty but don’t get any saltier.

57. What does the underlined word “evaporates” in Paragraph 3 mean?

A. turns into steam　　　　　　　　 B. turns into a solid

C. turns into fresh water　　　　　　　 D. turns into ice

58. From the passage we can know the seashells________.

A. get some minerals from seawater

B. take some salt from sea when seawater reacts with rocks

C. react with rocks of the ocean crust when plates move

D. absorb salt when the plates move

59. How many reasons does the writer mention why the oceans stay at about 3.5％ salt content?

A. 2　　 　　　　　　 B. 3 　　　　　 　　　 C. 4　　 　　　　　　 D. 5

60. What’s the purpose of the author to write the text?

A.　　 Warning　 　　 B. Informing　 　 C. Entertaining　　　 D. Describing

Answer 1

AABB