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If the adult child stay in USA, refuse to go to work (or or do business) and tax payment, or refuse to go to school, get something for nothing continue long period. Or when the adult child's permanent resident certificate will expire soon. Immigration Office will warn the adult child should go to work (or do business) and tax payment, or go to school. But if the adult child still ignore the relevant departments' warning. Immigration Office have right to revoke the adult child's permanent resident status, or refuse to replace new permanent resident certificate for the adult child, and should deport the adult child.