Which sentence uses they're correctly?

• A. Their going to the park.
• B. They're going to the park.
• C. Theyre going to the park.
• D. There's going to the park.

Answer: (D)

The main idea is choosing the correct contraction for they are. They’re is the contraction of they are, used when the subject “they” is doing the action. In this sentence, a group of people is the subject and the action is going to the park, so the natural form is they’re going to the park.

The other forms don’t fit. Their is a possessive pronoun used to show ownership, which doesn’t apply to the action of going. Theyre is a common misspelling (missing the apostrophe) and isn’t considered correct. There’s is a contraction for there is (or there has), which would not convey who is performing the action of going.