题目列表(包括答案和解析)
Before the first non-stop flight made in 1949, it ________ necessary for all planes to land for refueling.
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11.Before the first non-stop flight made in 1949, it ________ necessary for all planes to land for refueling.
A. would be B. has been C. had been D. would have been
A. would be B. has been C. had been D. would have been
Before the first non stop flight made in 1949, it ________ necessary for all planes to land for refueling．
A．would be
B．has been
C．had been
D．would have been
Before the first non-stop flight made in 1949, it ________ necessary for all planes to land for refueling．
would be
has been
had been
would have been
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