They were surprised that a child should work out the problem they themselves couldn't.A.

发布时间：2020-08-15 01:03:21


They were surprised that a child should work out the problem      they themselves couldn't.
A. once
B. then
C. While
D. if

网友回答

A. once
B. then
(答案→)C. While
D. if
解析：
while（implying a contrast）含相对之意，表示对比转折。
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