The values of a in the equation: \log_{10}(a^2 \minus{} 15a) \equal{} 2 are:
(A)\ \frac {15\pm\sqrt {233}}{2} \qquad(B)\ 20, \minus{} 5 \qquad(C)\ \frac {15 \pm \sqrt {305}}{2}
<spanclass=′latex−bold′>(D)</span>±20<spanclass=′latex−bold′>(E)</span>none of these