How does the overload principle apply to a successful fitness program?

How does the overload principle apply to a successful fitness program?
A. The overload principle helps individuals determine when their muscles have reached failure while exercising.
B. The overload principle allows people to chart their progress during a fitness program.
C. The overload principle helps individuals achieve consistent gains in their fitness program.
D. The overload principle instructs an individual to target certain body parts while exercising for optimal results.