Do you remember a certain occasion ________ you were in trouble and at that moment I gave you a hand?
A . which B . that C . when D . where
C
【解析】
【详解】
考查定语从句。句意:你还记得有一次你有困难的时候,我曾帮助过你吗?此处为定语从句修饰先行词 occasion ,先行词在从句中作时间状语,故用关系副词 when 引导。故选 C 。