[题目]-|||-如图,在点电荷q的电场中,选取以q为中心、R为-|||-半径的球面上一点P处作电势零点,则与点电荷q距-|||-离为r的P-|||-点的电势为 ()-|||-P-|||-R-|||-q r P-|||-A. dfrac (q)(4pi {varepsilon )_(0)r}-|||-B. dfrac (q)(4pi {varepsilon )_(0)}(dfrac (1)(r)-dfrac (1)(R))-|||-C. dfrac (q)(4pi {varepsilon )_(0)(r-R)} .-|||-D. dfrac (q)(4pi {varepsilon )_(0)}(dfrac (1)(R)-dfrac (1)(r))