Bone-strengthening physical activity done increases bone-mineral content and bone density in youth. a. four or more hours a day b. every weekend c. three or more days a week d. twice a week every two weeks

C) three or more days a week

Explanation:

Three days per week is the recommended intensity of physical activity required for youths, however, if it can be a little more than that, it will keep impacting positively on the subject.

Over-exercising is prejudicial that´s why it is not recommended to do considerably long sessions per day, better distribute it, on different days a week, with diverse activities that will allow and fortify the bone-mineral content and density.

The reason why is required physical activity practically daily for youth, is because its the age where the human ¨evolve¨ more. Bones, brain, muscles and all the organs are in a develop period, that´s why it´s required to foment this growing with physical activity, the synergy produced between these two aspects potentiates this process, leading to more physical satisfactory results as stronger bones, bigger and versatile muscles, etc.

d, i believe because of it's activity level

9, 5, 10000000 ( that is supposed to be a ten for the last one)