invitation question...

hi girls! i just got my invitations, and i have a really stupid question about the response cards... they come with envelopes printed with my name and address for the people to send them back to me... now.... when i send out the invitations, do i put the response card inside the little envelope or leave them separate?? thanks! i'm totally clueless

I would think to leave them separate.
ETA: tucked under the flap of the envelope

This site Verseit is chuck full of tips for all invitation questions!