2. 职称英语
  3. If the salinity (含盐量) of ocean waters is analyzed, it is found to vary only

If the salinity (含盐量) of ocean waters is analyzed, it is found to vary only

游客2024-02-28  33
问题     If the salinity (含盐量) of ocean waters is analyzed, it is found to vary only slightly from place to place. Nevertheless, some of these small changes are important. There are three basic processes that cause a change in oceanic salinity. One of these is the subtraction of water from the ocean by means of evaporation—conversion of liquid water to water vapor. In this manner, the salinity is increased, since the salts stay behind. If this is carried to the extreme, of course, white crystals of salt would be left behind; this, by the way, is how much of the table salt we use is actually obtained.
    The opposite of evaporation is precipitation (降水), such as rain, by which water is added to the ocean. Here the ocean is being diluted(冲淡)so that the salinity is decreased. This may occur in areas  of high rainfall or in coastal regions where rivers flow into the ocean. Thus salinity may be increased by the substraction of the water by evaporation, or decreased by the addition of fresh water by precipitation or runoff.
    Normally, in tropical regions where the sun is very strong, the ocean salinity is somewhat higher than it is in other parts of the world where there is not as much evaporation. Similarly, in coastal regions where rivers dilute the sea, salinity is somewhat lower than in other oceanic areas.
    A third process by which salinity may be altered is associated with the formation and melting of sea ice. When seawater is frozen, the dissolved(溶解) materials are left behind. In this manner, seawater directly beneath freshly formed sea ice has a higher salinity than it did before the ice appeared. Of course, when this ice melts, it will tend to decrease the salinity of the surrounding water.
    In the Weddell Sea, of America, the densest water in the oceans is formed as a result of this freezing process, which increases the salinity of cold water. This heavy water sinks and is found in the deeper portions of the oceans of the world. [br] The major topic discussed in the passage is ______.
选项 A、the subtraction of water
B、the conversion of liquid water to water vapor
C、the salinity of ocean water
D、the effect of precipitation on the salinity of ocean water
答案 C
解析 本文讲述的要点是海水的含盐量。本题主要考查对全文的理解和对中心的概括。此文主要围绕海水的含盐量进行叙述，列举了三种不同情况下含盐量的增减。因此最合适的答案为C。而A“水分的去除或减少”，B“水由液态转为固态”，和D“降水对海水含盐量的影响，”都只是文中叙述的一个方面，而不是主要观点。
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