Qingming Day is also a day people whose parents are dead visit the cemetery.AwhichB

问题补充：

Qingming Day is also a day people whose parents are dead visit the cemetery.

Awhich

Bthen

Cthat

Dwhen

答案：

A. which

B. then

C. that

(答案→)D. when

解析：考查定语从句。本定语从句的先行词是a day.定语从句的结构很完整，使用关系副词when.AC都是关系代词，then不是定语从句的关系词。句意：清明节是那些亲人去世的人去祭拜墓地的那一天。故D正确。