The main reason a person becomes a supervisor is

OK basically to become a supervisor you need key knowledge to know how to do so so the best option will be Work related knowledge 

To help people learn a certain trade, work, or to help beginners or minors in a job learn, replace, and succeed. A supervisor is someone who understands the trade/ work being done, and it is easier for them to help others than to actually be a part of the job/occupation. 

I hope this helped you!

Brainliest answer is always appreciated!