In a pulley setup that has a moving pulley,
a. you have to pull the string a greater distance, and it takes more work to lift the mass
b. your work doubles because the pulley moves
c. you have to pull the string a greater distance, but the force needed to lift the mass is cut in half
d. you don't have to pull very much to lift the mass

Explanation:

With a moving pulley you don't have to pull very much to lift the mass, because this pulley distributes better the weight, requiring a lower force to lift than using a simple pulley.

So, basically, in this type of system, the force needed is less, however, to know if is half less or even a minor proportion, we need to use specific values, that's why option C is not the answer, because with the data given, you cannot calculate if the force needed is the half.

thermal energy is the answer