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【多选题】
关于共振的防止和利用,应做到 ( )A.
利用共振时，应使驱动力的频率接近或等于振动物体的固有频率
B.
利用共振时，应使驱动力的频率大于或小于振动物体的固有频率
C.
防止共振危害时，应尽量使驱动力频率接近或等于振动物体的固有频率
D.
防止共振危害时，应尽量使驱动力频率远离振动物体的固有频率
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举一反三
【简答题】It' s cold outside. You' d better__________your coat.
【单选题】It’s _______ outside. Put on your thick coat to keep you_______.
A.
enough cold, hot
B.
cold enough, warm
C.
cold enough, warmly
D.
enough cold, warm
【单选题】Keep the door ______. It's too cold outside. [ ]
A.
closing
B.
closed
C.
to close
D.
open
【单选题】— It's cold outside. Put on your coat, ____ you may catch a cold. — OK, I will. [ ]
A.
and
B.
but
C.
or
D.
so
【单选题】It's very cold outside. You______ put on your overcoat.
A.
had better to
B.
would better to
C.
had better
D.
would better
【简答题】地貌旅游资源可以分为哪五大类?
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