--Have you ever visited the Shanghai World Expo?---YesWhen I was in China I

问题补充：

----- Have you ever visited the Shanghai World Expo?

-----Yes．When I was in China , I it twice．

A. have visited

B. visited

C. had visited

D. would visit

答案：

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。