With the verb have, always use opportunity. The word possibility is more often used with "there is":
There's a possibility I might move to England next year.
I have the opportunity to work in my company's London office.
Also, possibility is neutral - it means maybe the event will happen, and maybe it will not happen. The word opportunity is a little more positive, it expresses the possibility for something good. So we can use possibility with good or bad things, but opportunity is usually used only for good things:
I'm worried about the possibility of losing my job.
I have the opportunity to do a study abroad program.
You should take that job. It's a great opportunity for your career.
The word chance is more informal, and it can be used for possibilities or opportunities!
This project has so many problems, there's little chance of success.
Is there any chance of rain this weekend?
The boy got a chance to meet his favorite professional basketball player.
I was chosen to appear on the TV show! This is my chance to become famous! = my opportunity to become famous
Exercise also plays an important role in the treatment of depression
It not only keeps the body physically and mentally fit but also provides recreation and mental relaxation. It is nature' best tranquilliser. According to Dr. Robert Brown, a clinical associate professor at the University of Virginia School of Medicine," Exercise produces chemical and psychological changes that improves your mental health. It changes the levels of hormones in blood and may elevate your beta-endorphins(mood-affecting brain chemicals). Exercise may also improve the function of the autonomic nervous system."