Question 4 of 5 Marathon runners: A. can run only one or two marathons a year. B. only eat carbohydrates. C. tend to have more slow-twitch muscle fibers. D. are always very thin.

This question is about the characteristics of marathon runners. Let's analyze each option:<br /><br />A. Marathon runners can run only one or two marathons a year. This statement is not necessarily true. The number of marathons a runner can participate in depends on their training, recovery, and overall health, not just their status as a marathon runner.<br /><br />B. Marathon runners only eat carbohydrates. This is also not true. While carbohydrates are a crucial source of energy for marathon runners, they also need proteins and fats in their diet for overall health and muscle recovery.<br /><br />C. Marathon runners tend to have more slow-twitch muscle fibers. This is true. Slow-twitch muscle fibers are more efficient at using oxygen to generate energy for continuous, extended muscle contractions over a long time, which is beneficial for endurance activities like marathons.<br /><br />D. Marathon runners are always very thin. This is not necessarily true. The body composition of marathon runners can vary widely. Some may be lean, but others may have a more muscular build.<br /><br />Therefore, the correct answer is C, as it accurately describes a characteristic of marathon runners.