单项选择题

Not until the early years of the 19th century ______what heat is.

A．man did know
B．man knew
C．didn't man know
D．did man know
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单项选择题
—Do you know our town at all —No, this is the first time I ______here.,
A．was
B．have been
C．came
D．am coming
单项选择题
Peter______ come with us tonight, but he isn't very sure yet.
A．must
B．may
C．can
D．will
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