题型:选择题 如图所示,A、B两导体板平行放置,在t=0时将电子从A板附近由静止释放(电子的重力忽略不计)。分别在A、B两板间加四种电压,它们的UAB—t图线如下列四图所示。其中可能使电子到不了B板的是 : 查看答案
题型:选择题 This is the first time that I_____ to give a lecture to so large a audience till now. [ ]A. am invited B. have invited C. have been invited D. will be invited 查看答案