题目

阅读下列短文, 从每题所给的A、B、C、D四个选项中选出最佳选项。Girlscan easily get sad. If your friend is feeling blue and calls you, what will youdo? Here are some tips on how you can make her smile again. Listento her. When people feel sad, they often have the feeling of needing to be heard.So, listen carefully to what she is saying and do nothing else. Your friend willsurely thank you for being the shoulder she can cry on. Onceyou are done with listening, you can offer some advice or remain silent and lether feel everything and let it all out by crying. As a friend, 如图所示，在匀强电场中，将电荷量q＝5．0×10－10 C的正电荷，由a点移到b点和由a点移到c点，电场力做功都是3．0×10－8 J。已知a、b、c三点的连线组成直角三角形，ab＝20 cm，∠a＝37°，∠c＝90°，（sin37°=0．6 , cos37°=0．8）求：（1）a、b两点的电势差Uab（2）若（b=0，则（a=？（c=？（直接写出结果即可）（3）匀强电场的场强大小和方向。