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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If I had time, I ______ French.
A. will study
B. would study
C. shall study
D. would have studied
单项选择题
The flowers ______ sweet.
A. are smelt
B. smell
C. is smelt
D. smells
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