A、2x-ex
B、<img width="73" height="14" src="http://img.wangxiao.cn/examfiles/imgcache/attached/image/20140605/20140605154907_2827.png" />
C、<img width="73" height="14" src="http://img.wangxiao.cn/examfiles/imgcache/attached/image/20140605/20140605155800_5953.png" />
D、<img width="87" height="14" src="http://img.wangxiao.cn/examfiles/imgcache/attached/image/20140605/20140605155820_8342.png" />
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