Do we need "double indefinite article "an, a" in the following statements or can be omitted? Make it as a rule! Besides, which one is syntactically and semantically acceptable?
Is that an expression or an idiom
Or
Is that an expression or idiom
Or
Is that expression or an idiom
Or
Without
Is that expression or idiom
[motr]Thank you & Salam in advance[/motr]