目前，我国规定保护接地线为（）色。
A.黑
B.黄
C.绿
D.黄绿双
参考答案：D
You look tired. Why not stop ______? [ ]
A. to have a rest
B. having a rest
C. has a rest
D. have a rest
溃疡病常见的并发症有_____、_____、_____、_____。
