【题目】-- I heard that there are a few seats left for tonight's show.
-- Really? I was under the impression ______ they were sold out a long time ago.
A.what
B.which
C.that
D.where

【答案】C
【解析】句意：我记得很久以前他们被卖掉了。impression（印象），它后面是that引导的同位语从句，是具体内容。故选C。