问题
选择题
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
答案
C
while是并列连词,意为“而,却”,前后有对比的意味。
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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
C
while是并列连词,意为“而,却”,前后有对比的意味。