Last Sunday they reached Qingdao, ________ a conference was to be held．

Last Sunday they reached Qingdao, ________ a conference was to be held．

A.which

B.that

C.when

D.where

答案及解析： D

解析：

先行词是Qingdao，表示地点，要填where引导定语从句并在从句中作地点状语。