请问8老师父母绿卡后每年必须在美国住的时间必须多于6个月吗？如果是5个月多一点是否有问题？非常感谢~！
-The principle is that the green card is for them to live in US permanently, so they can not travel between US and China too often. If they want to live in China for a while, they may apply for the reentry permit.
