单项选择题

A million years ______ but a brief span in the history of our planet.

A．have been
B．are
C．is
D．has been
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单项选择题
Crisis would be the right word to describe the in many rare animal species.
A．restriction
B．descent
C．decline
D．minimization
单项选择题
No sooner had I told him the truth ______ that I should have remained silent.
A．than I had realized
B．than did I realize
C．when I realized
D．than I realized
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