回複：Pjiang和大俠們請教綠卡和回美證

一家三口廣州領館簽證，通過後可不可以爸爸先來，一陣子後媽媽再和兒子過來，
-可以. But all the family members have to enter U.S. before their immigration visa expires (the expiration date is indicated on the each visa).
還是一定要全家一起來？

另外，登陸後大概多久能收到綠卡？
-When they enter U.S., they become lawful permanent resident immidiately. They can file I-90 to get the physical card immidiately after they enter U.S. and may get it for a few months.
如果需要回國，保險起見，是不是可以辦回美證？
-if they plan to stay outside US for > one year 從申請回美證到拿到回美證，大概需要多久時間？
-Several months. But they leave US after they do the fingerpringting and before the RP approval.