单项选择题

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
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单项选择题
______the old man's sons wanted to know was ______ the gold had been hidden.
A．That, what
B．What, where
C．What, that
D．What, if
单项选择题
Without your help, we ______ such rapid progress.
A．couldn't make
B．wouldn't make
C．will not have made
D．wouldn't have made
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