三相四线制回路的中性线上必须安装熔断器。
参考答案：错
—Mom, when shall we go to Tian'anmen Square this weekend?
—Oh, sorry. I'm going to Shanghai for a meeting. _______ Saturday ______ Sunday is OK. [ ]
A. Neither; nor
B. Not only; but also
C. Both; and
D. Either; or
浓缩系统正常运行时，随着系统绝压的降低，浓磷酸沸点相应（）
A、升高
B、降低
C、不变
