—It was in 2015 ________ she was working as a volunteer in Africa.

A. thatB. which

C. whenD. then

【答案】C

【解析】

考查定语从句连接词。句意：——你什么时候认识你女朋友的？——是在她在非洲做志愿者的2015年。本句为定语从句修饰先行词2015，且先行词在从句中做时间状语，故用关系副词when。故选C。