移民局的回复：
Your appointment will not be rescheduled. Applicants are given two opportunities to appear at an oath ceremony. Alter two missed ceremonies, your case may be re-opened.
这个怎么re-open?
-1. If USCIS just close your N-400 case administratively (i.e., USCIS put your case on hold, not final decision yet) due to your missing the oath ceremony, then you may submit a written request to USCIS to reopen your N-400 case. The request should be submitted within one year of the date the case was closed. You do not need to pay any fee in this case. You should include supporting documentation to explain why you missed the oath ceremony. This could include medical records, proof of travel, or any other relevant evidences such as the proof of your request of the appointment reschedule (e.g., copies of your request by mail, email/online and USCIS responses to your request).
2. If you receive the N-400 denial notice (i.e., your N-400 is denied/revoked), you can file I-290B Motion to Reopen within 30 days from the date the denial notice is issued. You should include supporting documentation to explain why you missed the oath ceremony as I mentioned above. You need to pay the I-290B filing fee in this case.
3. Another choice is that you may file a new N-400. i.e., apply for the naturalization again, but this way may take more time and money.
Anyway, you need to read the USCIS letter carefully when you get it to see whether your N-400 is just closed (on hold) or it is denied. Then, take the action properly.
我6/30绿卡到期，得赶紧renew了吧？
-If you do not use the green card to travel abroad or find a new job before you get the US citizenship, you do not have to renew it.
