Nancy with her friend _________ now. [ ]
A. play
B. plays
C. is playing
D. are playing
答案:C
无力感产生后有三方面的表现()、()、()。
佛尔哈德法只能在()溶液中进行滴定。
A. 碱性
B. 酸性
C. 弱酸
D.强碱