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亲戚在三藩市，移民来美快三个月了，工卡收到了，但绿卡还没有收到。这样正常吗？

-Did you pay the immigrant fee yet? If no, they will never send the green card to your relative. If yes,  just contact USCIS for the status. 

Read this link about the immigrant fee payment:

https://www.uscis.gov/file-online/uscis-immigrant-fee