题目

一静止电子开始经电压为U1的加速电场加速后，又垂直于电场线进入电压为U2的两平行金属板间的偏转电场，射出偏转电场时沿电场线方向偏移量为y，要使y增大，则应：（  ）A、U1、U2都增大    B、U1、U2都减小    C、U1减小、U2增大   D、U1增大、U2减小  答案：C解析:略 We all know that,__________ ,the situation will get worse. [     ]A. not if dealt carefully withB. if not carefully dealt withC. if dealt not carefully withD. not if carefully dealt with