题目

如图所示电路,电源电动势为E、内阻为r,接通电路后A、B、C三盏小灯都达到一定的亮度(但均未达到额定功率),当滑动变阻器的滑动头P向左滑动时,则(                                                           )                                                                                                              A. A灯变亮,B灯变暗                 B. A灯和B灯都变暗     C. C灯和B灯都变亮                    D.   C灯变暗,A灯变亮                                                                                                                                   答案:C
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