Final answer:
b. The drum will rotate slower. When there is friction between the drum and the belt, the drum will rotate slower.
Step-by-step explanation:
When there is friction between the drum and the belt, the belt will slip on the drum. This is because the friction opposes the motion of the belt. As a result, the belt will not be able to effectively grip the drum, causing it to slip.
This slipping of the belt will lead to a decrease in the rotation speed of the drum. Therefore, the correct answer is b. The drum will rotate slower.