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Where Has the Salt Come from？

Every now and then， we meet a fact about our earth that makes us feel strange and no answer for the fact has yet been found. Such a fact is the existence of salt in the oceans. How did it get there？

We simply do not know how the salt got into the ocean！ We do know， of course， that salt is water-soluble， and so passes into the oceans with rainwater. The salt of the earth's surface is constantly being dissolved （溶解） and is passing into the ocean.

But we do not know whether this can explain the huge quantity of salt in oceans， if all the oceans were dried up， enough salt would be left to build a wall 180 miles high and a mile thick. Such a wall would reach once around the world at the Equator （赤道）！

The common salt that we all use is produced from seawater or the water of salt lakes， from salt springs （源泉） and from deposits of rock salt. The concentration （濃度） of salt in seawater ranges from about three per cent to three-and-one-half percent. The Dead Sea， which covers an area of about 340 square miles， contains about 11，600，000，000 tons of salt！

On the average， a gallon （加侖） of seawater contains about a quarter of a pound of salt. The beds of rock salt that are found in various parts of the world were all originally formed by the evaporation （蒸發(fā)） of seawater millions of years ago. It is believed that the thick rock-salt deposits were formed after about nine-tenth of the volume of seawater had been evaporated.

Most commercial salt is obtained from rock salt. The usual method is to drill wells （井） down to the salt beds. Pure “water is pumped down （抽進(jìn)去） through a pipe. The water dissolves the salt and it is forced through another pipe up to the surface.

16 We have not fully understood how salt got into the ocean.

A Right B Wrong C Not mentioned

17 The author is sure that the dissolved salt from the earth's surface is the only source of the huge quantity of salt found in oceans.

A Right B Wrong C Not mentioned

18 If all the oceans were dried up， the salt thus obtained would be extremely great in size.

A Right B Wrong C Not mentioned

19 The percentage of salt content in the Red Sea is higher than that in the Dead Sea.

A Right B Wrong C Not mentioned

20 Beds of rock salt are found in every part of the world.

A Right B Wrong C Not mentioned

21 After evaporation， about ten percent of seawater becomes rock salt.

A Right B Wrong C Not mentioned

22 Most commercial salt is obtained from seawater.

A Right B Wrong C Not mentioned

【參考答案】

1. A 2. B 3. A 4. C 5. A 6. A 7. B

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（責(zé)任編輯：vstara）

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