Marathon runners a) can run only one or two marathons a year b) tend to have more slow twitch muscle fibers c) are always very thin d) only eat carbohydrates

The correct answer is A.can only run one or two marathons a year. The reason behind this is running more than 2 is hard on the body and mind. It increases risk of injury and can slow your times for your end result.

What happens to the influenza virus every 20-40 years and why?