I didn't know you could do this until today: on the email app in OS X desktop, you can simply select a chunk of email body text and hit reply and the new message will contain only the selected text to reply to, in iOS, you do exactly the same thing, highlight the text you want and hit reply and the text will be included in the new message body!
Gotta love undocumented features!
Gotta love undocumented features!