Answer:
The answer is letter C, increasing the physical demands on the body over time.
Step-by-step explanation:
"Progressive Overload" is a principle that is commonly used by muscle gainers. This principle states that muscles will grow once the body is forced to adapt to a tension. This tension must be more than the tension he previously experienced.
This means that, if you are lifting 30 lbs. every day, nothing will happen to your muscles if you lift the same amount of weight for 10 years (provided that you also do the same repetitions).
In order to gain muscle, you have to increase the weight or increase the number of reps. This will allow your muscles to adapt to the new change and thus your body will also gain strength. It will also look more toned.
Thus, this explains the answer, letter C.