So my parents should leave the US in July and apply for I-485 in China. With their situation, you do not recommend us to apply greencard in the US this time, correct? Sorry for requesting your confirmation again, but this is such a critical topic, and I want to be sure before move onto any action. I thank you very much for your understanding, pjiang!
The further question is:
How about option (d): Can we apply for extension, assume their stay can be extended to October, can they go back to China in September, and then apply for I-485 in China? Is option (c) better than (d) or they are the same? Will option (d) cause any further complications?
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Option (c) - Parents leave in July. Apply greencard in China.
Option (d) - Apply extension here, stay till September. Go back to China in Septemember, and then apply greencards in China afterwards.