如图<img src="/lqwvjeImg/a7/a76c2ba0f49d3c3d0c7451419b573b91.png"style="width:164px;height:184px;">所示,两个“无限长”的、半径分别为R1和R2的共轴圆柱面,均匀带电,沿轴线方向单位长度上的所带电荷分别为<img src="/lqwvjeImg/4f/4ff1c35b98f7e330b947c907779956f6.png"style="width:51px;height:23px;">,则在外圆柱面外面、距离轴线为r处的P点的电场强度大小E为:( )<br>· <img src="/lqwvjeImg/2c/2ce983bdbdecd3a6482496707fd7e55f.png"style="width:51px;height:45px;">.<br>· <img src="/lqwvjeImg/91/9132775845c47080f1a5b82f2b83ce7b.png"style="width:186px;height:45px;">.<br>· <img src="/lqwvjeImg/ff/ff6bd234eaacfb02f4c76fb6d006152a.png"style="width:89px;height:45px;">.<br>· <img src="/lqwvjeImg/bd/bdf90ff60d2f206c8f0b133daccbe952.png"style="width:119px;height:45px;">.