Which one is it?

I have no use for questions that demand the top or single or one and only anything. Why do you have to have a yes or no?
For instance, if I am a quadriplegic, or 102 years old, or 2 days old, or just was in a horrible car wreck, or any number of situations, how 'single most important' is exercise?

(If this is homework, we don't do homework unless you try first..)

Is exercise the single most important thing YOU do?

False.

Breath. That is the single most important thing a person can do. If they don't do that then they'll die.

You can't expect anyone to give you an absolute true answer here do you? That'd be foolish.