They were surprised that a child should work out the problem____ they themselves could not. A．once B...
2022-12-08 16:45:58 32次 2015届黑龙江集贤县第一中学高一上学期期末考试英语试卷（解析版） 单项填空 反馈错误 加入收藏 正确率 : 100%
题目内容：
They were surprised that a child should work out the
problem____ they themselves could not.
A．once B．unless C．while D．if
本题链接：
