Mom made him _____ on the road.[ ]
A. not to play
B. not play
C. to playing
答案:B
You need _____ English if you want to have a good iob. [ ]
A. to know
B. know
C. knowing
D. knew
下面哪种方法不能消除六价铬()。
A、酸洗法
B、氧化还原法
C、离子吸附法
D、电解法