How do I add CC or BCC recipients to a reply?

Above the reply editor you will see the To row plus "CC" and "BCC" labels with a count of current recipients. 1) Click "CC" or "BCC" to open that field. 2) Type an email address or pick one from the list (the placeholder reads "Type email or select from list"); addresses already seen in the conversation are suggested. 3) Press Enter to add it. Invalid or duplicate addresses are removed automatically.