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  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  29
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] Which of the following statements is NOT TRUE according to the passage?
选项 A、Various factors combine to cause variations in the salinity of water.
B、As a result of the formation of ocean ice water salinity decreases.
C、The salinity of the water near the bottom of the oceans is relatively high.
D、in coastal areas the ocean is diluted by rivers.
答案 B
解析 要求我们对全文有充分的理解，并能记住有关细节，这样才能判断对错。A项：“不同的因素结合在一起改变了水的含盐量。”文中的确提到了各种不同的因素，如蒸发等去除水分的方法和降水等增加水分的方法，这些方法使世界各地水的含盐量有所不同。所以A项正确。B项“海水结冰的结果是使水的含盐量下降了。”而文中却提到海水结冰后，冰下的水含盐量增高。因此B项是不正确的，应选B项。c项：“靠近海洋底部的水的含盐量相对高一些。”文中第五段提到海水结冰后，冰下的水浓度高，所以下沉到海洋更深的部分。因此可以推出海洋靠近底部的海水的含盐量相对高一些。C项是正确的。不选C。D项“在沿海岸的地区，海洋被河水冲淡了。”这在文中第二段中有明确的表述。文中写到“增长的水会冲淡海洋。这可能发生在雨林地区或海洋地区，在沿海地区河水冲进海洋。”也就是说在沿海岸地区，海洋被河水冲淡了。所以D是正确的，不应选D。
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