饮用水的基本卫生要求不包括()。
A.净化消毒设施完善
B.感官性状良好
C.水量充足,取用方便
D.流行病学上安全
E.所含化学物质对人体无害
参考答案:A
The final test ____, all the students went home happily. [ ]
A. has been finished
B. finishing
C. finished
D. was finished
两个电容器并联,若C1=20μF,C2=30μF,则等效电容为()。
A.50μF
B.12μF
C.60μF
D.40μF