We know that if we have two languages produced by one regular grammar, then any language produced from the union, intersection, and so on would be regular.
What if we have a regular grammar that produces language A and a different regular grammar that produces language B. Then could the closure properties still be used in order to produce another regular language C?
For example, is $A\cap B$ a regular language (intersection)? Is $A\|B$ a regular language (concatenation)?