With a relative pronoun: The girl in the red dress______ is talk

With a relative pronoun: The girl in the red dress______ is talking to the teacher is Tom's sister.
【正确答案】：who
【题目解析】：定语从句，从句部分缺主语去，且主语为主句的girl ，因此关系代词要指代the girl ，选用who