Answer and Explanation:
Split system training is a program of weight training that divides training sessions by body regions—usually upper- and lower-body training. For example, your weight training program includes a lower-body split on Tuesdays and an upper-body split on Thursdays.
C. Delivers more oxygen to the body
I believe teens definitely are most concerned about muscular strength. They are more worried about that because they want to protect themselves, impress others, sometimes kids just want to bulk up to not look so wimpy, etc.
I would have to say teens are less worried about flexibility because when you have mussels why worry about doing the splits or putting your leg up to your head. One thing will always distract you from the rest.