主轴转速1350r/min、钻头直径Ø12，求切削速度
A. 50.9m/min
B. 60m/min
C. 55m/min
D. 90m/min
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“I don’t like to travel. ”“Have you ever _____ in an airplane?”
A. flying
B. flew
C. flowed
D. flown
The center of gravity of the human body ______ behind his joint.
A. located
B. locating
C. to locate
D. is located
“Today is very cold, isn’t it?” “Yes, the river is _____ over.”
A. freezed
B. freeze
C. frozen
D. freezing
“What happened in that new area?” “New houses ______ recently over there.”
A. are built
B. build
C. have built
D. have been built
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