6. A forward force acting on the axle accelerates a rolling wheel on a horizontal surface. If the wheel does not slide, the frictional force of the surface on the wheel is: (A) zero. (B) in the forward direction and does zero work on the wheel. (C) in the forward direction and does positive work on the wheel. (D) in the backward direction and does zero work on the wheel. (E) in the backward direction and does negative work on the wheel.
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