视频监控系统独立接地时对地电阻值应不大于（）
A.1Ω
B.2Ω
C.3Ω
D.4Ω
参考答案：D
Only when I read this story for a second time to appreciate its beauty.
A．had I began
B．that I began
C．I began
D．did I begin
新鲜与陈旧性关节脱位的时间界限是（）。
A.1～2周
B.2～3周
C.3～4周
D.5周
E.5～6周
