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【单选题】
Every means ________ tried, but we still cannot solve this problem.
A.
is
B.
have been
C.
are
D.
has been
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参考答案：
参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】If he had been willing to go with us, we _____ all his expenses.
A.
must have paid
B.
must pay
C.
would have paid
D.
should have paid