A point charge $+Q$ is at the center of a spherical conducting shell of inner radius $R_{1}$ and outer radius $R_{2}$, as shown in $\underline{\text { Figure } 16-25 . \text { The charge on }}$ the inner surface of the shell is
A. $+Q$.
B. $-Q$.
C. 0 .
D. $+Q / 2$.
E. $-Q / 2 .$ SSM