多谐振荡器是一种自激振荡电路，不需要外加输入信号，就可以自动地产生矩形脉冲。（ ）
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One morning there was a ______ on John's door.
Show me the tools and I'll be able to do a job that _____ you.
You are quite a _____ to build this bridge after all I've said and done.
The students are expected to hand in their _____ this weekend.
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