Question

complete the sentence with the best relative pronoun.

in 1886, president grover cleveland married frances folsom, the daughter of his friend and law partner; frances, □ was only twenty - one at the time, became the youngest first lady in u.s. history.

Explanation:

The sentence has a non - restrictive relative clause "____ was only twenty - one at the time" modifying the proper noun "Frances". In non - restrictive relative clauses that refer to people, the relative pronoun "who" is used as the subject of the clause. "Whom" is used as an object, "which" is for non - human antecedents, and "that" is not used in non - restrictive relative clauses. So the correct relative pronoun is "who".

Answer:

who