Thank you all for your replys.
Sometimes my questions may sound silly. Please don't laugh at me.
===Please have forms filled out prior to (before ) approaching th window
? Can I substitue prior to with before?
? I know prior to is a kind of formal usage. but is there any other
differences between this two ?
You could say 'before' there. They mean the same, but, as you say, 'prior to' is more formal.