Which word means 'belonging to them'?

• A. There
• B. Their
• C. They're
• D. Theirs

Answer: (B)

Belonging to them is shown by a possessive form that modifies a noun. The word that fits this use is their, a possessive determiner placed before a noun to show ownership: their car, their idea, etc. It directly answers “whose?” with a noun following.

The other options don’t fit that role: there is is a location word; they’re is a contraction of they are; theirs is a possessive pronoun used in place of a noun (as in The car is theirs). So for a phrase where you want to say something belongs to them and you’re about to name the thing, use their.