Answer:C..net work done on the object.
Explanation:
Since the elevator is moving with a constant speed and not accelerating, the tension in the string is simply the normal, routine, everyday boring weight of the object. Since the elevator is moving with a constant speed and not accelerating, the tension in the string is simply the normal, routine, everyday boring weight of the object.
We can calculate the density of the balloon as follows:

Therefore, the balloon will fall
Since the density of air is about 0.00123 g/cm^3 , the balloon is much more dense than the surrounding air. As a result, the balloon weighs more than the air that it displaces so the balloon will fall.
The lithosphere includes the crust, and the mantle :)