The correct answer is B. their.
The pronoun “their” refers to the third person plural, which means it can be used to refer to a group of people or things that are not the speaker or listener. In this case, the pronoun “their” is used to refer to the people who bought the new furniture.
The pronoun “mine” refers to the first person singular, which means it can be used to refer to the speaker. In this case, the pronoun “mine” would not be correct because the speaker is not the one who bought the new furniture.
The pronoun “ours” refers to the first person plural, which means it can be used to refer to the speaker and the listener. In this case, the pronoun “ours” would not be correct because the speaker is not the one who bought the new furniture, and the listener is not mentioned in the sentence.
The pronoun “yours” refers to the second person singular or plural, which means it can be used to refer to the listener or a group of people that includes the listener. In this case, the pronoun “yours” would not be correct because the listener is not mentioned in the sentence, and the group of people that includes the listener is not the one who bought the new furniture.