单项选择题

Not until the early years of the 19th century ______ know what heat is.

A．did man
B．man did
C．have man
D．man have
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单项选择题
It has been ten years since she ______ a nurse.
A．is
B．has been
C．was
D．had been
单项选择题
Tom is ______ taller than Mike.
A．very
B．much
C．as
D．rather
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