Question

complete the sentence with the best relative pronoun. i just read about an after - school program started by mr. brennan, i once had as a teacher.

Explanation:

We need a relative pronoun to refer to Mr. Brennan (a person) in the non - restrictive relative clause. The relative pronouns for people in non - restrictive clauses are "who" or "whom". Since "Mr. Brennan" is the object of the verb "had" (I once had Mr. Brennan as a teacher), "whom" is the appropriate choice.

Answer:

whom