Answer: Vitamins
Explanation:
Vitamins play a very vital role in the human system, they are considered as essential nutrients which perform hundreds of roles in the body, some of those roles are building the bones, healing wounds, strengthen the immune system, repair damaged cells and conversion of food to energy. It's function spans into 13different category.
All of the above Because You work on it any time else and your bones wont be as strong as you grow older if you work on it all the time you have stronger bones
Answer:
Upper level
Because no one can see it but its still good and far less expensive.