51单片机共有4个8位的并行I/O口，其中P2口既可用作地址/数据口，又可用作一般的I/O口。
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Frankly, I'd rather you ______ anything about it for the time being.
A. do
B. don't do
C. didn't do
D. will not do
In Britain, the best time for sighting is ______ spring and early summer.
A. later
B. latter
C. last
D. late
It may be five to ten years ______ we can test this medicine on human patients.
A. since
B. after
C. before
D. when
Thirty minutes ______ the limit of this interview.
A. are
B. have been
C. is
D. has been
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