受电弓滑板上升和下降至同一高度时,静态接触压力差不大于()N。
A、15
B、17
C、19
D、21
参考答案:A
The workers will go on strike if the demands they put forward are turned down. [ ]
A.could
B.would
C./
D.had
简述新闻评论的群众性特征。