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根據USCIS網站，file I-130 online，file I-485 by mail，附上I-130的receipt 同樣算concurrent filing.不知我的理解是否正確

-Not true. Concurrent filing means I-130 and I-485 are filed at the same time, i.e., send the documents for these two cases  at the same time.

Of course, you can file I-130 online and then, file I-485 (either online or by paper) after you receive the I-130 Receipt Notice. But the mailing address for I-485 filing by paper may be different in this case. Check I-485 Instructions.