母亲当年疲于每六个月中美间奔波，就决心回去了。如果明年想来美国探亲，届时回国三年多了，请问：
1.绿卡是否自动作废了
-Yes.
2.是否必须申请B-2签证才能来美国
-She had better abandon the green card at any one of the US Consulates in China, and then apply for B-2 visa at the same time or later to come to US.
3.B-2签证前是否必须签署放弃绿卡的文件 -Yes. Provide the completed I-407. See:
http://beijing.usembassy-china.org.cn/abandonment-of-status.html
http://www.immihelp.com/greencard/abandonment-greencard.html
4.有无可能不签放弃绿卡的文件并能拿到B-2签证，来美后是否可以将绿卡延续或更新？-No. But you can sponosr her to apply for the green card again as you did before after she enters US using B-2 visa.
还是这种情况没有可能。
5.如果放弃绿卡了，将来再申请，需要等一段时间吗？如果需要，要等多久？-The same procedure and processing time as you did for her before. It seems she may not want to live US permanently (this is common for many senior Chinese who are not used to the US life), she may not need to have the green card, and just use the B-2 visa to visit you.
谢谢。很折腾，但也很无奈。。。这种情况有无更好的建议？
