user: ### NOW ANSWER:
Question: Name the number of high rebounds for April 21
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, 'April 19', '@ Indiana Pacers', 'W 103-100', 'P. Pierce (40)', 'P. Pierce (11)', 'P. Pierce (6)', 'Conseco Fieldhouse', '1-0']
SQL:

assistant: SELECT COUNT("High rebounds") FROM "Table" WHERE "Date" = 'April 21';