【题目】He wrote a letter __________ he explained what had happened in the accident.
A. what B. which
C. where D. how
在线课程【答案】C
【解析】句意：他写了一封信，信中他解释了事故中发生了什么。本题考查定语从句。从空格处到句尾是定语从句，修饰先行词letter。将先行词代人从句后为：He explained what had happened in the accident in the letter. 由此可知从句中缺少状语，应该用关系副词where，相当于in which。