4. B。主旨题。第二段的第一、二句The most widespread mistake of all is that colds are caused by cold.
They are not.是本文的主题句。全文主要阐述了“感冒不是由寒冷引起的”这一观点。
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Zinc(锌) is one of about 20 elements necessary
for good health. It is present in the body in a very small amount but makes it
possible for important chemical actions to be carried out in cells. Scientists
are just beginning to discover how zinc and other elements work.
Researchers
first studied zinc as a way to speed recovery. Dr. Waltor Powys formerly with
the United States Air Force noted that the laboratory animals recovered faster
when some matters were added to their food. One of these matters was zinc. Dr.
Powys later tested the zinc treatment on an American airman recovering from
medical operations. The airman who received zinc sulphate(硫酸盐) recovered in half of the usual time.
Other doctors studied persons who had a number of strange disorders. The
doctors learned that all of these problems were caused by lack of zinc in the
body. They treated these disorders successfully by giving the patients zinc
sulphate.
The
amount of zinc in the body can be found by examining blood and hair. A lack of
this important element is not uncommon among people in both industrial and
developing countries. Zinc is found in most high protein(蛋白质) foods such as meat, milk, fish and
eggs. It is also found in whole grains. But many people do not eat enough of
these food. Food markets should add these elements so that more people could
get needed amount of these necessary matters.