17一个未带电的空腔导体球壳,内半径为R。在腔内离球心的距离为d处 (dlt R) ,固定一点电荷 +9 如图所示。用导-|||-线把球壳接地后再把地线撤去。选无穷远处为电势零点,则球心O处的电势为()。-|||-R d-|||-0 +q-|||-(5.0分)-|||-A、 .-dfrac (9)(4pi {varepsilon )_(0)R}-|||-B、 dfrac (q)(4pi {varepsilon )_(0)}(dfrac (1)(d)-dfrac (1)(R))-|||-C、0-|||-D、 .dfrac (q)(4pi {varepsilon )_(0)d}