1.我的绿卡12月过期，我应该提前半年还是90天申请，我看移民局的网站也没说清楚。因为I-90有一个选项是：my existing green card has already expired or will expire within 6 months.
-You can file I-90 in advance up to 6 months before your green card expires.
2. 我可以离开美国，在12月之前回来吗？
-Yes.
还是我要申请新绿卡拿到stamp才可以离开美国-If you file I-90 before your green card expires, your green card will be extended for one year when you conduct the biometrics (talk to the IO at that time).
