A car hoist is filled with oil. Why would it be different to use if it were full of air?

Okaaay, this is for my grade 8 science class. We're learning about fluids, and this is one of the questions for the test tomorrow. The teacher gave us the answer sheet but it got cut off at the side so you can't read it properly. Anyone know the answer? PLEASE HELP, I NEED TO PASS :(:(:(