The answer would be pubic hair. Because, secondary sexual characteristics.
Visible secondary sex characteristics are nonreporductive sexual characteristics.
For males things that will start to show are pubic hair, facial hair, and Adam's apple.
The basis for physical fitness is having a good eating habit, which means to know what you are eating and to eat cleanly. Exercise at least an hour every day and drink plenty of water throughout the day.
It's D because first thing you do when you are aging into a adult is find a job
