A、X<sub>1</sub>-X<sub>2</sub>+X<sub>3</sub>
B、2X<sub>3</sub>-μ
C、<img src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/c443ce35-9fcb-4e3b-b8ca-cb38e73fbcc2.jpg" width="66" height="46" />
D、<img src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/771d86e9-2654-4dcb-9288-b40426dbed5c.jpg" width="71" height="58" />
E、<img src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/2a7a9e18-0cf1-4959-ab5a-3d975c6413c7.jpg" width="29" height="40" />