The boy, . . . . . . . . father is a doctor, is my friend. A. which B. who C. whom D. whose

The correct answer is: D. whose

The word “whose” is a relative pronoun that is used to introduce a clause that describes the possessor of something. In this case, the clause “whose father is a doctor” describes the boy.

The other options are incorrect because they are not relative pronouns. The word “which” is a relative pronoun that is used to introduce a clause that describes a thing. The word “who” is a relative pronoun that is used to introduce a clause that describes a person. The word “whom” is a relative pronoun that is used to introduce a clause that describes a person as the object of a verb or preposition.

Here is a diagram that shows how the sentence can be parsed:

[The boy] [whose father is a doctor] [is my friend].

The boy is the subject of the sentence. Whose father is a doctor is a relative clause that modifies the boy. Is my friend is the predicate of the sentence.