Almost all English prepositions look like verbs.
A. when they turn into Chinese
B. when turning into Chinese
C. when they turned into Chinese
D. when turned into Chinese
网友回答
A. when they turn into Chinese
B. when turning into Chinese
C. when they turned into Chinese
(答案→)D. when turned into Chinese
解析：本题考查分词作状语，逻辑主语为English prepositions，与turn into之间的关系为被动关系，故用过去分词，选D。