问题
选择题
Measures must be taken before there is another collapse of the coal mine, ______?
A．must they
B．mustn’t they
C．is there
D．isn’t there
答案
答案：B
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Measures must be taken before there is another collapse of the coal mine, ______?
A．must they
B．mustn’t they
C．is there
D．isn’t there
答案：B