单选题
The students didn"t manage to work out the problem ______ their teacher had explained how.
A、
when
B、
until
C、
unless
D、
as
【正确答案】
B
【答案解析】
[解析] 句意:直到老师解释了这道题的做法,同学们才把它做出来。固定用法题。not...until...表示“直到……才……”。
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