It's not C. There should be a comma where the semi colon is
Andrea because she is the most focused. Tom is acting either immature which is not a good quality in a leader. Whilst Joe is not confident and is acting shy which is also not a good quality for a leader.
I believe that it means we never know our full potential, and that we never know how great we are till we are asked to show it.
A pretty long time I would say
