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NO.37
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题目来源 : 填空经典1500题
Select one entry for the blank. Fill the blank in the way that best completes the text.

The theory that the 1908 Tunguska event was the explosion of a cosmic body in the sky over Siberia is _____: no one has yet found fragments of the object or any impact craters in the affected region. 

long-standing
indisputable
plausible
uncontested
unproven

Select one answer choice.

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