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: should be "whose" instead of "who's" (who is).
-
Don't forget to pack your coat and hat, because its going to be snowing in Minnesota all week.
- Correction: should be "it's" (it is) instead of "its" (possessive form of it).
The correct answers are the second and fourth sentences.