2. 外语
  3. In fact, even without humans, the Earth’s climate changes. Some climate change is【C1】______. But, as greenhouse gases are added

In fact, even without humans, the Earth’s climate changes. Some climate change is【C1】______. But, as greenhouse gases are added

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问题     In fact, even without humans, the Earth’s climate changes. Some climate change is【C1】______. But, as greenhouse gases are added to the atmosphere, human influence "emerges" from natural variability.
    Droughts, one of the most intensely studied climate events, are a perfect example of a(n) 【C2】______with both natural and human influences. Separating the【C3】______strengths of the influences is a challenge for scientists. However, with the large social and economic costs of droughts, it is a challenge the scientists must【C4】______.
    In a very recent study published in the Journal of Climate, authors Richard Seager and Martin Hoerling cleverly used climate models forced by sea surface temperatures to【C5】______how much of the past century’s North American droughts have been caused by ocean temperatures, natural variability and human influences.
    Droughts can be caused by a(n) 【C6】______of separate or interactional phenomena. At its root, drought results from the low【C7】______of water falling and sometimes higher temperatures(which increase evaporation rates). The beginning of drought can often be linked to variations in ocean temperatures.
    It is also found that the oceans can affect the atmosphere to create conditions that are【C8】______responsible for drought. What’s more, temperature increases【C9】______with human-driven global warming also play a role. This【C10】______agrees with other researchers who have shown that, while human-emitted greenhouse gas warming may not cause a particular drought, it can make drought come on earlier, faster, and harder than it otherwise would.
A)associated
B)attached
C)conclusion
D)conduct
E)distinguish
F)effect
G)natural
H)partly
I)quality
J)quantity
K)relative
L)ridiculous
M)simply
N)undertake
O)variety
【C6】
选项
答案O
解析 空格位于不定冠词a(n)与介词of之间，故应填入名词。根据下文的separate or in—teractional phenomena可知，干旱是由各种各样独立的或相互作用的现象造成的，故空格处应填入variety“种类”。a variety of意为“各种各样的，种种”。备选的名词中，conclusion“结论”、conduct“行为”、quality“质量”和quantity“数量”均不符合文意，故排除。
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大学英语四级

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