新警察就是搞不清楚这几个机构的作用是什么，他们之间是什么关系？
National Visa Center (NVC): A private company located in Portsmouth, New
Hampshire that processes certain immigration filings under contract with the
U.S. Department of State (DOS). In appropriate cases, NVC receives approved
green card petitions from USCIS or DOS and continues the green card process
by sending forms and instructions to the applicant, receiving the forms and
supporting documents back from the applicant, and then forwarding the
applicant’s file to the proper U.S. embassy or consulate abroad.
U.S. Citizenship and Immigration Services (USCIS): An agency of the
Department of Homeland Security (DHS) responsible for ruling on immigration
and naturalization matters and establishing immigration policies and
priorities. USCIS was formerly called the Immigration and Naturalization
Service (INS) and was part of the U.S. Department of Justice. On March 1,
2003, INS transitioned into DHS. Thus, INS no longer exists.
USCIS functions include adjudication of immigrant visa petitions,
adjudication of naturalization petitions, adjudication of asylum and refugee
applications, adjudications performed at the service centers, and all other
adjudications formerly performed by the INS.
Department of State (DOS)
