题目

阅读理解 AnnaliseEmerick is getting ready to play a show in Nashville, Tennessee. It issomething she does most nights in coffee houses, bars and other small spacesacross the U.S. But tonight, Ms. Emerick will play for a few people in KristinaShulz's home. Ms.Shulz has been holding such performances in her home for about four years. Asmany as 30 people have attended past shows. The crowd is usually a mix offamily, friends and neighbors. But some strangers might show up, too. Theperformances are listed on house concert websites. We've done rock, we'vehad blues, pop, folk, we'll have anything空间有平行于纸面的匀强电场，一电荷量为—q的质点（重力不计），在恒定拉力F的作用下沿虚线由M匀速运动到N，如图所示，已知力F和MN间夹角为θ，MN间距离为d，则 （       ）A．MN两点的电势差为B．匀强电场的电场强度大小为C．带电小球由M运动到N的过程中，电势能减少了D．若要使带电小球由N向M做匀速直线运动，则F必须反向