在I/O口中，P2口在接LED时，必须提供上拉电阻。
查看答案
51单片机的P0.0引脚是该芯片的32脚。
A. 对
B. 错
单片机引脚封装类型大体上都一样。
A. 对
B. 错
1. At that time, _________ that it had been so hard for them to start a small business.
A. never did they realize
B. never they realized
C. never have they realized
D. never they have realized
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