Which sentence uses 'they're' correctly?

• A. Their going to the concert tomorrow.
• B. They're going to the concert tomorrow.
• C. There going to the concert tomorrow.
• D. Theyre going to the concert tomorrow.

Answer: (B)

The correct form uses the contraction that stands for they are. In this sentence, the subject is they and the verb phrase is are going, describing a plan for the near future, so they’re going to the concert tomorrow reads naturally and is properly punctuated with the apostrophe to show the missing letters.

The other options mix up common homophones or omit the apostrophe: their is a possessive determiner, so “Their going” would be grammatically off; there indicates location or existence, so “There going” lacks the necessary auxiliary; theyre is not the standard written form of the contraction without the apostrophe.