The two sentences that include errors in the use of possessives or contractions are:
-
We are not certain who's textbooks these are, but we want to find out so that we can return them.
- Correction: "who's" should be "whose" (possession).
-
Don't forget to pack your coat and hat, because its going to be snowing in Minnesota all week.
- Correction: "its" should be "it's" (contraction for "it is").