单项选择题
You cannot master a foreign language（）you work hard at it.
A．unless
B．if
C．when
D．so
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相关考题
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单项选择题
Those who won't work should be made（）
A．worked
B．work
C．to work
D．to be working -
单项选择题
It is high time that you（）your work.
A．begin
B．began
C．will begin
D．has begun -
单项选择题
Must I hand in the paper right now No, you（）
A．mustn't
B．can't
C．needn't
D．shouldn't
