问题

(2013·高考新课标全国卷Ⅰ)There’s no way of knowing why one man makes an important discovery________another man，also intelligent，fails

A:since
B:if
C:as
D:while

正确答案是：

同类题型

_____, you’ll never be able to persuade him. [ ]

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d you _______ a drink—No, thanksI have given updrinking

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