Mason should (B) increase the speed at which he runs, because he is at practice and is simply told for how long he can run, but not at which pace. He wouldn't make a great impression on his coach if he ran for too long and missed out on important exercises. Thus, it would be better for him to just speed up as that increases his heart rate. Additionally, if he were to decrease either the time or the speed at which he runs he would only lower his heart rate.