Which sentence uses a contraction or possessive form incorrectly?
a. the blue house on the corner is theirs
b. do you know whether they're lost?
c. your cousin is on my softball team
d. i'm not sure who's purse is on that chair

The sentence that used contraction or possessive form incorrectly is letter (D) I'm not sure who's purse is on that chair. The word that makes it wrong is "who's." The word who's is a contracted form of "who is." In the sentence, the correct word that should be used is "whose" because "who's
" does not fit correctly in the sentence.

Fill with evil is the answer

The answer would be a.