80.
Why is Washington, D. C. the most
important American city? Because ___.
A. it is the largest city
B. it is the largest in population
C. it is the most beautiful city D. it is
the capital of the United States
C
There is a
definite(绝对的)possibility
that the climate(气候)of the world may be changing. Some scientists imagine that this
could even mean the beginning of another ice age. The effects of such a change
in climate on the human population of the world would be startling(惊人的).
Recent
research suggests that the general warming trend(趋势)of the past hundred years or so may be coming to an end. During
the past ten years, meteorologists tell us the average temperature of the earth
has dropped about one degree Fahrenheit. This does not seem like much, but it
could have effects on wind and rain patterns which influence the overall
weather picture. If these patterns(形式)change a lot, it could mean that certain regions of the world may
continue to have long droughts(干旱)while others will possibly suffer from widespread flooding.
What
regulates(调节)the climate
is not exactly known. Meteorologists believe that clouds may be an important
factor(因素)in
regulating the amount of solar(太阳的)heat held by the earth, which in turn determines the temperature
of the planet. Another possibility is that man’s industrial and agricultural
methods may be affecting the natural weather patterns. However, the weather is
not understood well enough for scientists to say for certain what is happening
to the climate and what side effects this will actually have on the word’s
population.