一、匹萍题-|||-1.在点电荷 +9 的电场中,若取图 2-1 中P点处为电势零点,则M点的电势为 () 。-|||-(A) dfrac (q)(4pi {varepsilon )_(0)a} (B) dfrac (q)(8pi {varepsilon )_(0)a} (C) dfrac (-q)(8pi {varepsilon )_(0)a} (D) dfrac (-q)(4pi {varepsilon )_(0)a}-|||-0-|||-q P M-|||-a a-|||-图 ... ... 1-|||-R1-|||-0-|||-R2-|||-图 2-2