2011职称英语考前每日一练［卫生类B级－第18期］

　　第2部分：阅读判断（第1～7题，每题1分，共7分）

　　下面的短文后列出了7个句子，请根据短文的内容对每个句子做出判断：如果该句提供的是正确信息，请选择A；如果该句提供的是错误信息，请选择B；如果该句的信息文中没有提及，请选择C。

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 （浓度） 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 （加仑） 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 （蒸发） 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 （抽进去） 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.