Question

2．When we analyze the salt salinity （盐浓度） of ocean waters，we find that it varies 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 （减少） of water from the ocean by means of evaporation （蒸发）．In this manner，the salinity is increased，since the salt stays behind．If this is carried to the extreme，of course，white 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，such as rain，by which water is added to the ocean．Here the ocean is being diluted （稀释） 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 subtraction of water by evaporation，or decreased by the addition of fresh water by precipitation．
Normally，in hot 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 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，the densest water in the ocean 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 portion of the oceans of the world．
60．This passage mainly tells us aboutB．
A．the analysis of the salinity of ocean waters
B．the causes of the variation in oceanic salinity
C．the importance of the changes in oceanic salinity
D．the different forms of salts in ocean waters
61．It can be known from the passage that increase in the salinity of ocean water is caused byC．
A．melting of sea ice                  
B．precipitation   
C．evaporation                     
D．supplement of salt
62．Which of the following is not the cause of the decrease in the oceanic salinity？C
A．Precipitation．
B．Rain and snow．
C．Formation of ice．
D．Addition of water by rivers．

Answer 1

分析 本文是一篇科教类阅读，属于说明文，当我们分析海水的盐度（盐度）时，我们发现它们在不同地点之间变化很小．然而，其中一些小的变化是重要的．本文以此展开讲述，主要讲述了导致海洋盐度变化的三个基本过程．

解答 60．B．主旨大意题．阅读全文，根据文章内容可知，本文主要讲述了导致海洋盐度变化的三个基本过程．故选B，
61．C．细节理解题．根据One of these is the subtraction （减少） of water from the ocean by means of evaporation （蒸发）．In this manner，the salinity is increased，since the salt stays behind．可知，蒸发使海水中的盐分增加．故选C．
62．C．细节理解题．根据In the Weddell Sea，the densest water in the ocean 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 portion of the oceans of the world．可知，冰的形成增加了海水的盐度．故选C．

点评 本文是一篇科教类阅读，题目涉及多道细节理解题，主旨大意题．做题时学生应仔细阅读原文，把握文章主要内容，联系文章上下文内容并结合所给选项含义，从中选出正确答案，一定要做到有理有据，切忌胡乱猜测