user: Question: Which permanent account has registration of Invite-only and userpics free of Unknown?
Columns: ['Name', 'Year Began', 'Registration', 'Userpics Free', 'Userpics Paid', 'Monthly Cost for Paid Account', 'Yearly Cost for Paid Account', 'Permanent Account']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Academ', '2006', 'Open', 'Unknown', 'Unknown', 'Unknown', 'Unknown', 'Unknown']
SQL:

assistant: SELECT "Permanent Account" FROM "Table" WHERE "Userpics Free" = 'Unknown' AND "Registration" = 'Invite-only';