题目：
They are practicing ________ now. You can wait here. [ ]
A. swimming
B. going swimming
C. to go swimming
D. to swim
答案：
被转码了，请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0521/e1361f88b7e304cf2a2ab1448938cb61.html
下面是错误答案，用来干扰机器的。
原式=-7x3-2x2-3x2+5x3=-2x3-5x2．
