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【简答题】
请你设计两个能说明声音产生原因的实验． 实验一：______，______． 实验二：______，______．
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举一反三
【简答题】aware of/conscious of how the infection happens 翻译
【单选题】If something seldom happens, it
A.
happens every day
B.
does not happen often
C.
happens on purpose
【简答题】You see the lightning _________ it happens, but you hear the thunder later. A) the instant B) for an instant C) on the instant D) in an instant
【单选题】______________ the day before yesterday. [ ]
A.
something happens to him
B.
He happens to something
C.
Something happened to him
【单选题】If anything the machine, please let us know.
A.
happens on
B.
happens to
C.
happened on
D.
will happen to
【单选题】If anything __________the machine, please let us know. [ ]
A.
happens on
B.
happens to
C.
happened on
D.
happen to
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