Which of the following changes would reduce the magnitude of the torque on a bolt by the greatest amount, assuming wrench length, force magnitude, or angle are altered individually and all other factors remain unchanged?
a) Reducing the wrench length by 25%
b) Changing the pulling angle from 90∘ to 30∘
c) Changing the pulling angle from 90∘ to 60∘
d) Reducing the force magnitude by 25%