Final answer:
When lifting a box with constant velocity, the force you are lifting with is zero.
Step-by-step explanation:
When you are lifting a box with constant velocity, the force you are lifting with is D) Zero force.
Lifting a box with constant velocity means that there is zero acceleration. According to Newton's second law of motion, F = ma, where F is the force applied, m is the mass of the box, and a is the acceleration. Since the box is not accelerating, the force you are lifting with is zero, which means it is equal to the weight of the box (mg), but with opposite direction.
Therefore, the correct answer is D) Zero force.