Answer:
The sentence using correctly who as a relative pronoun is option A. the salesman who sold it to me was effective.
Explanation:
Relative pronouns are the ones used in a sentence to refer to nouns mentioned previously, whether those names correspond to people, things (places and ideas) or animals. In English the most common relative pronouns are who, whom, whose, which, that. As well as whoever and whomever.
Bearing in mind the described above, the relative pronoun who is used to refer a person mentioned previously. In the particular case of the example provided the pronoun "who" is being used to refer to "the salesman"
