What's SECRETLY Killing Your Vitamin C?

Vitamin C is very sensitive and is destroyed very easily. And this happens even before we put it in our mouth. Why does this happen? What destroys vitamin C. In this video:
3 important reasons why vitamin C is destroyed.
How not to destroy vitamin C?
In what form is vitamin C better absorbed by the body?
What elements should vitamin C not be combined with?
What vitamins can vitamin C be combined with?
What vegetables have a lot of vitamin C?