Since my mom's medical exam was not ready when we sent her GC application, we sent the exam after we got the letter requiring it. In pjing's blog, he mentioned, 移民局来找你，是通过 RFE 的方式。通常，移民局会提供一个预印的信封，供你回邮。
But the letter sent us didn't include the 预印的信封, does it matter?
-Does not matter, but you need to enclose the USCIS request for evidecne letter (keep the photocopy for your record) with your response and the required documents in the packet and send them to USCIS before the deadline.
Also, he mentioned "所有表格、文件都是单面打印（No Double Side)". Unfortunately, I didn't know that when I was preparing the application, some material, such as tax forms, I used double side.
-It is also fine.
I don't know if this will affect the process of my mom's application. It didn't mention in any letters they sent us so far.
-It is fine.
Should I make an appointment with local infopass asking them about my mom's AP?
-Fine.
