超声波的产生是由（）单元送来的触发脉冲输入到发射电路上产生高频电脉冲激励探头晶片产生的。

A.电源

B.同步

C.接收

D.放大

根据句子的意思，补全单词。

1. The boy _____ a stone at the dog and then the dog ran away.

2. We'll do it _____  to the teacher's instructions (指示).

3. The town was destroyed in the war, but the library _____ .

4. As we know that the White Snake is a popular _____ .

5. The baker bakes his bread in the _____ .