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
Add 2 cups water with a 1/4 teaspoon of sea saltand or a half teaspoon of baking soda in one of your nostrils. Have your head tilted to the side so that the water comes out the other nostril. Its best used when youre experiencing nasal congestion.