Okay everyone, here's the answer:
There are usually two armrests. But that doesn't mean there are two armrests for every seat. If there are 10 seats in a row that means there are eleven armrests, most usually, but in some theaters there are only 9 cupholders. So if you are sitting between 2 armrests that means of course if no one is sitting next to you, that you can use any armrest you d____ well please, or both if you like! :)
