When a bicycle is in motion horizontally, the force of friction exerted by the ground on the two wheels can be
(A) In the backward direction on the front wheel and in the forward direction on the rear wheel
(B) In the forward direction on the front wheel and in the backward direction on the rear wheel
(C) In the backward direction on both front and the rear wheels
(D) In the forward direction on both front and the rear wheels

In cycling, the rear wheel moves by the force communicated to it by pedalling while front wheel moves by it self. So, while pedalling a bicycle, the force exerted by rear wheel on ground makes force of friction act on it in the forward direction (like walking). Front wheel moving by itself experience force of friction in backward direction (like rolling of a ball). [However, if pedalling is stopped both wheels move by themselves and so experience force of friction in backward direction].