题目信息
Despite their numerous attempts to do so, scientists have not been able to sustain a controlled nuclear fusion reaction.
A:their numerous attempts to do so, scientists have not been able to
B:their numerous attempts to do it, scientists have not been able to
C:them numerously attempting to do so, scientists have not been able to
D:their numerously attempting to do so, scientists cannot
E:their numerous attempt to do so, scientists were not able to
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共享解析来源为网络权威资源、GMAT高分考生等； 如有疑问，欢迎在评论区提问与讨论
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已选答案：
正确答案：
A:their numerous attempts to do so, scientists have not been able to
it只能指代名词或者做形式主语(it is)，排除B
再根据句子意思尝试很多次仍然不能够维持一个受控制的核聚变反应堆。过去式是发生在过去的，但是直到现在这件事其实都还没成功，现在仍然在进行。过去的动作或状态持续到现在，用现在完成时，选A
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题目来源
Manhattan
