user: Question: What is High Rebounds, when Location Attendance is "Madison Square Garden Unknown", and when Date is "May 18"?
Columns: ['Game', 'Date', 'Team', 'Score', 'High points', 'High rebounds', 'High assists', 'Location Attendance', 'Series']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'May 9', '@ New York', 'L 95–111', 'Alonzo Mourning (27)', 'Alonzo Mourning (13)', 'Muggsy Bogues (8)', 'Madison Square Garden Unknown', '0–1']
SQL:

assistant: SELECT "High rebounds" FROM "Table" WHERE "Location Attendance" = 'Madison Square Garden Unknown' AND "Date" = 'May 18';