下列哪项不能被认为是混凝作用机理？（）
A.电解质水解
B.电性中和
C.吸附架桥
D.网捕
参考答案：A
已知命题：“如果a＞0，b＞0，那么ab＞0”，则它的逆否命题是______．
In winter the small town is often _____ from the rest of the world. [ ]
A. cut up
B. cut down
C. cut off
D. cut in
