In a circle with center O, chord AB equals chord AC. Chord AD cuts BC in E. If AC \equal{} 12 and AE \equal{} 8, then AD equals:
<spanclass=′latex−bold′>(A)</span>27<spanclass=′latex−bold′>(B)</span>24<spanclass=′latex−bold′>(C)</span>21<spanclass=′latex−bold′>(D)</span>20<spanclass=′latex−bold′>(E)</span>18