user: Question: what are all the gtc winners for pole position No. 21 Team Modena
Columns: ['Round', 'Circuit', 'Date', 'Length', 'Pole Position', 'GT3 Winner', 'GTC Winner']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Oulton Park', '7 April', '60 mins', 'No. 1 Barwell Motorsport', 'No. 23 Christians in Motorsport', 'No. 81 Team Tiger']
SQL:

assistant: SELECT "GTC Winner" FROM "Table" WHERE "Pole Position" = 'No. 21 Team Modena';