选择题The policeman asked the man ——near the school on such a dark night

这里就牵涉到直接引语转间接引语时，人称的转换问题。规律是：一随主，二随宾，三不变。

一随主：直接引语中的第一人称在间接引语中应改成和主句的主语相一致的人称。例如：
He asked,"Where can I put the books?"
----He asked where he could put the books.

二随宾:直接引语中的第二人称在间接引语中应改成和主句的宾语相一致的人称。例如：
"what's your name?" the teacher asked the boy.
----The teacher asked the boy what his name was.(his和主句中的宾语the boy相一致)

三不变：直接引语中的第三人称在间接引语中保持不变。例如：
He says, "She is a worker."
----He says she is a worker.(she保持不变)

您的这道题原直接引语应该是：
The policeman asked the man，"What are you doing near the school on such a dark night?"
按照“二随宾”原则，自然应该选b。

选b what he was doing 做ask 的宾语，是间接引语，人称要转换，改成和the man 相一致的人称。答案d是直接引语的写法，所以不选

是间接引语 所以人称就要换成是间接人称