Jane has been so _______ in getting used to everything that she hasn’t had time for social activities.

A．confused

B．worried

C．devoted

D．occupied

右图是等离子体发电机示意图，平行金属板间匀强磁场的磁感

应强度 B=0.5T，两板间距离为0.2m，要使输出电压为220V，

则等离子体垂直射入磁场的速度v₀=      m/s，a是发电机

的         极。 (发电机内阻不计)