CREATE TABLE table_58668 ("Date" TEXT, "Tournament" TEXT, "Surface" TEXT, "Opponent in the final" TEXT, "Score" TEXT)

What is Surface, when Tournament is 'Sunderland , United Kingdom'?
SELECT "Surface" FROM table_58668 WHERE "Tournament" = 'sunderland , united kingdom'
SELECT "Surface" FROM "table_58668" WHERE "Tournament" = 'sunderland , united kingdom'