If the new safety system _______ to use, the accident would never have happened.
A:had been put
B:were put
C:should be put
D:would be put
设x∈0,2π,且1-sin2x=sinx-cosx,则( )
1931年,在革命形势和中共的任务问题上,党内有些人继续强调全国性的“革命高潮”,党在全国范围的“进攻路线”,争取实现“一省或数省的首先胜利”。这种想法( )