Select the sentence that uses "they're" correctly.

The sentence "They're more likely to do well if they study" uses "they're" correctly. "They're" is a contraction of "they are," which fits perfectly in this context as it conveys the intended meaning that a group of people (the students) has a higher chance of succeeding if they engage in studying. This demonstrates a grammatical understanding of how contractions function in relation to their expanded forms. The use of "they're" here appropriately reflects a condition regarding their potential behavior or performance.