What is the primary factor that determines the amount of work done against friction?

The primary factor that determines the amount of work done against friction is indeed the distance moved in the direction of the force.

Work is defined as the product of the force applied along the direction of movement and the distance over which that force is applied. In the context of friction, when an object is moved against a frictional force, the work done to overcome this force is calculated as the frictional force multiplied by the distance the object travels while the friction is acting on it.

If the distance is greater, then the work done against friction increases, even if the force remains constant. This relationship highlights the direct influence distance has on work, making it the key factor when calculating work done against friction. Other factors, such as mass, time, and speed, can affect the frictional force or how quickly an object moves, but they do not directly impact the calculation of work done against that friction when considered in isolation. Thus, the correct option focuses on the essential component of the work formula in this context.