Coming of age, Puberty, and Responsibility.
I believe the answer is -Reduces the risk of many diseases, including cancer-
I would say "avoid over-training". I would say that this would most likely be the correct answer due to the fact that over working your body would be putting your body under too much work that you can really handle. And as you do that, when the real game happens, you could have to sore bones, and thus, this would then lead to an injury.
True. Lactic acid is caused by strenuous exercise. The lactic acid is formed because while working out, you don't receive as much oxygen.