They were surprised that a four-year-old boy should work out such a difficult problem the

发布时间：2020-08-17 13:15:29

They were surprised that a four-year-old boy should work out such a difficult problem      they themselves couldn’t.
A. once
B. then
C. while
D. if

网友回答

A. once
B. then
C. while
D. if
解析：while是并列连词,意为“而,却”,前后有对比的意味。  
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