He wrote a letter he explains what had happened in the accident.
A. what
B. which
C. where
D. how
网友回答
A. what
B. which
(答案→)C. where
D. how
解析：句意为：他写了一封信。在信中他解释了事故中发生的一切。据分析，“he explains what had happened in the accident.”部分为一定语从句，修饰先行词a letter。而且该从句本身主(he )--谓(explains )--宾(what had happened in the accident)成分齐全，缺少的是地点状语。所以用关系副词where.
【考点定位】定语从句的考查。