Before joining the Department of Defense, Mr． Panetta _______ as director of the CIA from February 2009 to June 2011．A.would serveB.servedC.was servedD.had been served
网友回答
B解析考查时态。根据本句的时间状语：from February 2009 to June 2011说明在过去的时间发生的事情，使用过去时即可。Serve没有被动语态。故B正确。