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(单选题)
By “…challenges explanation” (Para. 1) the author means that _____.

(本题4.0分)
A、
no explanation is necessary for such an obvious phenomenon


B、
No explanation has been fade up to now


C、
it.s no easy job to provide an adequate explanation


D、
it.s high time that an explanation was provided

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出自：哈尔滨师范大学-高级英语2（专升本）

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