—Was it there you were away to see your friend off?
—I’m not sure . But when I got back, it was gone.
A. that
B. which
C. where
D. while
网友回答
A. that
B. which
C. where
(答案→)D. while
解析：句意：当你出去送别朋友的时候，它在那里吗？我不确定，但是，当我回来时，它就不见了。while 当…时候，引导时间状语从句，其余答案不符合题意，故选D