Final answer:
In the absence of friction, the force required to pull the masses at a constant velocity up the inclines is equal to the gravitational force acting on the masses.
Step-by-step explanation:
The correct answer is B: A force equal to the gravitational force acting on the masses. In the absence of friction, the force required to pull the masses at a constant velocity up the fixed inclines is equal to the gravitational force acting on the masses. This is because there is no force opposing the motion, so the force needed to overcome the gravitational force is equal to it. To maintain a constant velocity, the pulling force must precisely balance this component of the object's weight, therefore no net force is acting on the object, resulting in zero acceleration.