receipt number on I-797A for booking visa appointment

I only have a copy of I-797A. I am confused when they ask for my receipt number on I-797. Do they actually mean I-797A? The girl on the phone only repeated I-797 no matter what I said.

Do I need to get the original copy of I-797C from my lawyer as well? Is it required when you enter U.S.? I remembered the officer requested that when I entered U.S. from Canada with a F-1 visa.

Thank You very much,