A door is pushed by a constant force of magnitude F at a point located a horizontal distance r from its hinge. The force makes an angle θ with the plane of the door. Which of the following single changes would double the magnitude of the torque on the door while all other variables remain unchanged?
a) Doubling the magnitude of the force F while halving the distance r
b) Doubling the distance r at which the force is applied
c) Increasing the angle θ from 30∘ to 60∘ while keeping F and r unchanged
d) Increasing the distance r by 50%