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如果积累了一段时间, 然后拿白卡在境外待, 或者不用白卡而是每过6个月回美一次, 请教老师哪一种情况积累的入籍时间会被中断而需从头开始 ?
-It is irrelevant to the reentry permit. If you stay outside US for > 6 months, your residence continuity may be disrupted and if > one year, it will be disrupted no matter whether you have the reentry permit.

谢谢您 !

(有没有其他办法?)
-Exception for some cases:
http://bbs.wenxuecity.com/immigration/592939.html