----- Have you ever visited the 2010 Shanghai World Expo?
-----Yes．When I was in China , I it twice．
A. have visited
B. visited
C. had visited
D. would visit
网友回答
A. have visited
(答案→)B. visited
C. had visited
D. would visit
解析：考查时态。句意：你曾经参观过2010年的上海世博会吗？——是的。当我在中国时，我参观过两次。可知下文描述的是在过去某个时间发生的动作，故用过去时态。选B。