Answer:
C <em>cycling</em>
Explanation:
I'm saying cycling because everyone learned how to ride a bike at a young age and even if you don't know how to ride, you can put on training wheels. (lol). Hiking could be another good alternative but in case you get worn out, theres no place to call to get picked up because of bad service.
Pulling a wagon uphill; the more uphill the wagon is, the greater amount of energy that will be exerted when the wagon moves downhill.
