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
Tom ought not to ______me your secret, but he meant no harm.
A．have told
B．tell
C．be telling
D．having told
单项选择题
No sooner than it began to rain heavily.
A．the game began
B．has the game begun
C．did the game begin
D．had the game begun
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