Does recapping a soda bottle prevent flatness?

Let's say you are going to drink a bottle of soda over the course of two hours.

Which soda would be more flat?
A) One where you put the cap back on after every sip.
B) One where you keep the cap off during the lifetime of the soda.

Of course, you would say option B. Because it would seem that placing the cap back on would help prevent flatness. But every time you open the bottle back up, you hear some fizz being released. Perhaps there is some atmospheric difference between the carbonated beverage and the air. And recapping the bottle constantly agitates that difference.