A ball is thrown straight up into the air. If we do not ignore air resistance, the acceleration of the ball as it is traveling upward is....?

a.) 9.8m/s^2
b.) greater than 9.8m/s^2
c.) less than 9.8m/s^2
d.) zero
…
My line of thinking is that if there were air resistance, then the ball would travel slower. Therefore I thought the answer would be less than 9.8m/s^2. Correct answer is greater than 9.8m/s^2. Can somebody explain? Thanks.