He’ll never forget his stay in the park he found his cellphone which had gone missing days before.
A. that
B. when
C. where
D. which
网友回答
A. that
(答案→)B. when
C. where
D. which
解析：考查定语从句：句意：他永远忘不了在公园逗留的期间，那时他发现了几天前丢失的手机。先行词是his stay，表示时间，定语从句中缺少时间状语，选B。