A、P
B、-P
C、<img width="35" height="23" src="http://admintk.100xuexi.com/UpLoadImage/2016-09-30/afa1bd06-6e81-4e44-9169-a6219ca024df.png" />
D、-<img width="35" height="23" src="http://admintk.100xuexi.com/UpLoadImage/2016-09-30/afa1bd06-6e81-4e44-9169-a6219ca024df.png" />
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