单项选择题

Only (within) the past 200 years (scientists have) found (out what) fire (is).

A．within
B．scientists have
C．out what
D．is
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单项选择题
He (kept) his (head); (otherwise) the accident (had happened)
A．kept
B．head
C．otherwise
D．had happened
单项选择题
My father (enjoys) fresh (air), (sunshine), and (to take) long walks.
A．enjoys
B．air
C．sunshine
D．to take
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