Air drag is the frictional force which is due to air molecules and it is always opposite to the direction of motion
So here direction of air resistance is always opposite to the motion or velocity
Now if Car is travelling then the force on the car due to engine is always in the direction of velocity of car
Because here engine will provide the force to accelerate the car.
So opposite to that motion there is air resistance.
So here correct answer will be
B) The forward force applied by the engine