—He ought ot have been warned of the danger.

—____, but he wouldn’t listen to me.

A．yes, he ought to

B．So he was

C．So was he

D．So it was with him

（12分）如下图所示，一个电子以4×10⁶m/s的速度沿与电场垂直的方向从A点飞进匀强电场，并且从另一端B点沿与场强方向成150°角方向飞出，那么，A、B两点间的电势差为多少伏？(电子的质量为9.1×10^－31kg)