Can you think of an occasion you can use this gesture.A. whichB. thatC. whenD. on that

问题补充：

Can you think of an occasion you can use this gesture.

A. which

B. that

C. when

D. on that

答案：

A. which

B. that

(答案→)C. when

D. on that

解析：考查定语从句。句中先行词为occasion，在从句中作时间状语，故用关系副词when，选C。