Answer: C) they're, their.
Step-by-step explanation: homophones are words that have similar or identical sounds but they have different meanings, grammatical uses or spelling, which can cause confusion when using them. A very common group of homophones is "they're," "their," and "there,"the first one is the contraction of "they are" which is the conjugation of the verb "to be" in third person plural; the second one is a possessive pronoun used to describe belonging and the third one means "in that place." So the correct sentence would be "If they're locked out of their house, they should call me and I will let them in.