通水试验时,室内排水立管及水平干管,安装结束后均应作通球试验,通球球径不小于排水管径的(),顺利通过为合格。
A.1/4
B.2/3
C.3/4
D.4/5
参考答案:D
Bill was listening to the radio while Ann ______ TV.
A. watched
B. was watching
C. has watched
D. had watched
油品储运中有哪些污染问题?如何采取防止措施?