A dog is standing in the bed of a pickup truck. The bed is coated with ice, causing the force of friction between the dog and the truck to be zero. The truck is initially at rest, and then accelerates to the right, moving along a flat road. As seen from a stationary observer (watching the truck move to the right), the dog:

A. moves to the right at the same rate as the truck, so it doesn't slide.
B. does not move left or right, but the back of the truck moves towards the dog.
C. moves to the right, but not as quickly as the truck is moving to the right, causing it to slide towards the back of the truck.
D. moves to the left, as the truck moves to the right, causing the dog to slide towards the back of the truck.