@SIRAK I sent my application with all original documents (passport and citizenship certificate) with prepaid envelope separate for returning the citizenship certificate. Leave a note inside the return envelope stating that please send me back my citizenship certificate in this envelope after verification. I sent it last month and just received my citizen certificate today in the mail. You can do either priority or express. I did priority coz it cost only $6 compared to $20 express via usps. Its just a matter of 2 days.