Okay, an antecedent of a pronoun is always a noun, so immediately you can reject the words late and wandered as incorrect answers, because late is an adjective, and wandered is a verb. This leaves us with two nouns, guests and party. Obviously, the pronoun several refers to the noun guests, so the correct answer is guests - that is the antecedent that corresponds with the pronoun. Several guests, not several parties.
