1）我是不是可以理解成，如果儿子能够在母亲的非法居留时间少于180天的情况下提出绿卡申请，那末回美证就可以和绿卡一起申请？
-Yes. She can use AP to travel as long as her unlawful presence is less than 180 days when she files I-485.
2）如果母亲黑下来了，儿子还没有来得及给母亲申请绿卡。因为特殊原因母亲需要回中国去然后母亲就回去了。那末母亲就有在美国非法滞留的历史。以后在签证问题上母亲就会有你所说的3-year or 10-year bar。但是当儿子拿到公民后，给在中国的母亲申请绿卡，这个历史污点会影响母亲的绿卡申请吗？
-Yes. As long as her unlawful presence is less than 180 days when she files I-485, she will be sujected to 3-year or 10 year bar if she leave US before she gets her green card. It is less than 180 days, she will be OK to get the immigration visa in China.
3）如果母亲黑下来了，儿子也已经开始了母亲的绿卡申请。因为特殊原因母亲需要回中国去然后母亲就回去了。那末这已经开始的绿卡申请会出现什末问题？
-Same answer as for 2).
