连词成句。

1. by, we, going, train, are (.)

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2. to, China, a, have, we, trip (.)

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3. Palace Museum, we, to, go, the (.)

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4. stay, my, they, with, three, weeks, family, for (.)

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超声探头的换能作用是（）.

A.电能转换成光和热

B.电能转换成机械能

C.机械能转换成电能

D.机械能转换成辐射

E.声转换成超声