If a and b are positive numbers such that a^b \equal{} b^a and b \equal{} 9a, then the value of a is:
<spanclass=′latex−bold′>(A)</span>9<spanclass=′latex−bold′>(B)</span>91<spanclass=′latex−bold′>(C)</span>99<spanclass=′latex−bold′>(D)</span>39<spanclass=′latex−bold′>(E)</span>43