The correct answer is D. Specifity
Explanation
The principle of specificity is the name given to a principle of sports training that, as its name implies, states that physical qualities must be trained in the specific conditions that competition demands. That is, you have to train what you are going to compete, or as similar as possible. This is based on the biological fact that adaptations occur on the specific organs and systems that we train. According to the above, the best way to develop strong leg muscles for running is to train the muscles under the principle of specificity, because it is already known that you want to strengthen the muscles, the muscle group that you want to strengthen (the leg muscles), and what is the purpose of training (to sprint). So, the correct answer is D.
