题目选项分析

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.

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