诚心请教我现在在中国，1）如果移民签证下来了，我放弃不来会不会影响以后的旅游或探亲签证？
-It should be fine. Explain it if asked.
2）如果来美，是否必须得呆在美国半年才能回中国？
-You can visit China any time, but had better not stay in China for more than 6 months, not for more than one year.
3）如果提早回中国，是不是就违反规定了？
-No.
4）在美国这半年是一年中累计的半年还是一次性必须呆足半年？可以一年中多次往返凑足半年吗？谢谢了。
-The principle is that the green card is for you to live in US permanently. It is fine for you to visit China occasionally, but you can not use the green card as the border-crossing card to go forth and back between US and CHina too often.
So, if you don't plan to live US permanently, you may not need to apply for green card.
