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
Some areas, their severe weather conditions, are hardly populated.
A．due to
B．in spite of
C．but for
D．with regard to
单项选择题
She won't contact you, ______ something unforeseen happens.
A．as
B．since
C．though
D．unless
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