I have ?'s re CD's and DVD's that I want to ask [View all]

somewhere where they won't product large guffaws at my techno-ignorance/innocence.

Here goes:

Can one distinguish a CD and DVD by looking at it?

If I put a DVD in my CD player will it play (of course I can't see anything, but will I hear the audio?)

If I put a DVD in my CD player will it harm it?

Remember -- no guffaws.
thanks.