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 (q)(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}