Despite their numerous attempts to do so, scientists have not been able to sustain a controlled nuclear fusion reaction.
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Atheir numerous attempts to do so, scientists have not been able to
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Btheir numerous attempts to do it, scientists have not been able to
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Cthem numerously attempting to do so, scientists have not been able to
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Dtheir numerously attempting to do so, scientists cannot
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Etheir numerous attempt to do so, scientists were not able to
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正确答案: A