题目内容

超声波加工，不能加工硬脆材料。

A. 对
B. 错

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______into use in April 2000，the hotline was meant for residents reporting water and heating supply breakdowns.

A. Put
B. Putting
C. Having put
D. Being put

—Tom is never late for work. Why is he absent today?—Something _______to him.

A. must happen
B. should have happened
C. could have happened
D. must have happened

最小的语音单位是

A. 音素
B. 音节
C. 音位
D. 声母

汉语拼音方案中的声母有多少个？

A. 20
B. 21
C. 23
D. 26