Answer:
They're still not finished with the project that was due yesterday.
Step-by-step explanation:
Homophones are words with the same pronunciation but different meaning. The name of this phenomenon is homophony. Probably one of the most known examples of homophony are English words they're, their, and there, which often get mixed up because of their identical pronunciation. Still, it is important to know the difference between them.
They're is a contraction of words they and are. It is correctly used in the first example: They're still not finished with the project that was due yesterday.
There is an adverb meaning in or at that place. It is also a pronoun introducing a clause or a sentence. Correct examples of its use would be sentences I think I saw an entire flock of wild parrots sitting in the trees over there (there as an adverb instead of their) and There (there as a pronoun instead of their) are a number of great books about the Civil War in the library.
Their is the possessive form of the pronoun they. A correct example would be They said they would put away all of their (instead of there) clean clothes before school.