In a public area of computers, I am using a computer. I leave and make some copies temporarily. When I return, some people are approaching the computer, thinking that it is idle; so what tense would be used to tell them?:
-I was/am/have been using the computer.
I think they are all logical, but I am not sure whether there's one particularly natural and idiomatic.
Thank you. J.
In a lot of places these days, those people would be met with an angry shout of "Oy! I'm on that one!" It's not polite but it gets the message across.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
As they haven't reached the computer, I would using I am using, but was using is also OK. As it's about who has the right to the computer, have been using doesn't work as well for me.