大全987-142

   As U.S. nuclear attack submarines prowl their familiar haunts deep within the oceans of the world these days, they increasingly are engaged in missions far different from the tasks for which they were built and for which their crews were trained over the last forty years.

(A) they increasingly are engaged in missions far different from the tasks for which they were built

(B) the missions they increasingly engage in are far different than the tasks they were built for

(C) they engage increasingly in missions that differ significantly from the tasks they were built for

(D) the missions they engage in are increasingly different than the tasks for which they were built（A）

(E) they increasingly engage in missions far different than the tasks for which they were built

Please help, I don't know why A is better than E.  难道 "different than" 不行吗?  lus E is using active voice, which sounds better.