A:or
B:unle
C:but
D:whether
Mothers holding jobs outside the home should have ________ schedules to make it easier to care for their children. ( )
小王大笑时由于用力过猛,使上下颌不能合拢,这是由于( )
如图所示,平行板电容器与直流电源连接,下极板接地.两板间距为d,一带电油滴位于电容器中央的P点且恰好处于平衡状态.现将平行板电容器的下极板竖直向上移动 d3 ,已知重力加速度为g,则( )