To answer this question, we need to understand the pronoun usage in English.
In the sentence, "Her uncle is a doctor, isn't ___?", we are looking for the pronoun that correctly refers to the uncle.
Option A) "it" - This option is incorrect because "it" is used to refer to objects or animals, not people.
Option B) "he" - This option is correct because "he" is the appropriate pronoun to refer to a male person, which is the case with the uncle.
Option C) "you" - This option is incorrect because "you" is used to refer to the person being spoken to or addressed, not someone else.
Option D) "me" - This option is incorrect because "me" is used as the object of a verb or preposition, not as a pronoun to refer to someone else.
The correct answer is Option B) "he". This option is correct because "he" is the pronoun that correctly refers to the uncle.