回复：keep 绿卡

What is the requirement to keep 美国绿卡? My sister has got 绿卡 and she still has a job in China. Someone told me that she should stay in China less than half year at one time.
-She can apply for the reentry permit and then, she can stay in China for a maximum of two years continuously with this reentry permit. But she needs to file the tax return each year as usual.