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  3. The oceans have always served as a sink for carbon dioxide, but the burning of fossil fuels since the beginning of the industria

The oceans have always served as a sink for carbon dioxide, but the burning of fossil fuels since the beginning of the industria

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问题     The oceans have always served as a sink for carbon dioxide, but the burning of fossil fuels since the beginning of the industrial revolution, especially over the last 40 years, has given them more than they can【S1】______absorb. The result is that the oceans are becoming acid—a change in the【S2】______balance that threatens the oceans’ web of life.
    In earth’s history, there have been many【S3】______of acidification, mainly from volcanic eruptions (火山喷发). According to a new research review by pale oceanographers at Columbia University, published in Science, the oceans may be【S4】______acid far faster than at any time in the past 300 million years.
    Changing something as【S5】______as the PH of seawater has profound effects. Increased acidity attacks the shells of shellfish and the skeletal foundation of corals (珊瑚), dissolving the calcium carbonate (碳酸钙) they’re made of. Coral reefs are among the most diverse ecosystems on the planet. Ocean acidification【S6】______the corals and every other【S7】______that makes its living on the reefs.
    The authors tried to determine which past acidification events【S8】______the best comparison to what is happening now. The closest analogies are disastrous events, often associated with intense volcanic ac tivity resulting in major extinctions. The difference is that those events【S9】______thousands of years. We have acidified the oceans in a matter of decades, with no signs that we have the political will to slow, much less halt, the【S10】______.
A) absolutely I) process
B) animals J) safely
C) changing K) species
D) chemical L) transmitted
E) covered M) threatens
F) episodes N) turning
G) fundamental O) urgent
H) offer
【S6】
选项
答案M
解析 空格位于名词ocean acidification和the corals之间，由此可判断该句结构为主谓宾，故空格处应填入动词。根据文意，海洋酸化会威胁到海洋生物，因此应选择threatens“威胁”。
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