单选题 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 of water
from the ocean by means of evaporation. 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 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, sea- water 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.
单选题
This passage mainly tells us about ______.
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
【正确答案】
B
【答案解析】[解析] 本题考查文章大意，根据“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.”,“The opposite of evaporation is precipitation.”和“A third process by which salinity may be altered is associated with the formation and melting of sea ice.”可知，本文主要讲的是引起海水盐度变化的原因。
单选题
It can be known from the passage that increase in the salinity of ocean
water is caused by ______.
A. melting of sea ice
B. precipitation
C. evaporation
D. supplement of salt
【正确答案】
C
【答案解析】[解析] 根据第一段“One of these is the subtraction of water from the ocean by means of evaporation. In this manner, the salinity is increased.”可知，答案为C，即海水蒸发可使盐度增加。
单选题
Which of the following is not the cause of the decrease in the oceanic
salinity?
A. Precipitation.
B. Rain and snow.
C. Formation of ice.
D. Addition of water by rivers.
【正确答案】
C
【答案解析】[解析] 本题采用排除法。根据第二段“The opposite of evaporation is precipitation...so that the salinity is decreased.”，“in areas of high rainfall”和“in coastal regions where rivers flow into the ocean”可以排除A、B、D项，答案选C。
单选题
Which of the following statements is TRUE according to the passage?
A. Oceanic salinity has great effect on sea life.
B. Many factors combine to cause changes in oceanic salinity.
C. The movement of the water is related to the amount of salt.
D. The temperature of the water has much to do with the oceanic
salinity.
单选题
The purpose of mentioning the Weddell Sea is ______.
A. to give an example of cold-water salinity
B. to point out the location of deep waters
C. to make a comparison between hot-water salinity and cold-water
salinity
D. to show that the water in the Weddell Sea varies in salinity from place
to place
【正确答案】
A
【答案解析】[解析] 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.”可知，Weddell Sea是作为一个例子，说明this freezing process引起盐度变化，答案为A。