Answer:
a. Specificity
Step-by-step explanation:
The principle of specificity is an exercise principles which dictates that all of the training regiments that a person do should be designed to achieve a specified goals.
For example,
Let's say that Mark's goal is to be a professional soccer player. To achieve his goal, he should not spend the majority of his time lifting weight since muscular strength wasn't the main physical requirement to be good at the sport. He should design his training to improve his cardiovascular strength and his technique/dexterity.