I don’t know .
A. what happened to him
B. what did he happen
C. what he happened
D. what was the matter
网友回答
(答案→)A. what happened to him
B. what did he happen
C. what he happened
D. what was the matter
解析：考查宾语从句。特殊疑问句做宾语时，应用陈述句语序，可排除A，D选项语序不变，但是时态应用一般现在时态。what happened to sb，表示某人怎么了，句意：我不知道他怎么了。故选A