祝大家圣诞节快乐，请教各位1个问题，绿卡持有者，每年必须在美国住满几天？有人说180天，有人说9个月，也有人说半年回一次美国就可以了，都是道听途说，还是来这里问问专业人士，谢谢！
-You can not stay outside US for > one year continuously unless you have reentry permit. If you travel between China and US too often, you may have trouble at the port of entry even if you only stay in China for a few months each time. Please remember the green card if for you to live in US permanently, not for you to use it as a border-crossing card.
-You can not stay outside US for > one year continuously unless you have reentry permit. If you travel between China and US too often, you may have trouble at the port of entry even if you only stay in China for a few months each time. Please remember the green card if for you to live in US permanently, not for you to use it as a border-crossing card.
