CREATE TABLE table_41021 ("City of license" TEXT, "Identifier" TEXT, "Frequency" TEXT, "Power" TEXT, "Class" TEXT, "RECNet" TEXT)

Which class has a frequency of 91.9 fm?
SELECT "Class" FROM table_41021 WHERE "Frequency" = '91.9 fm'
SELECT "Class" FROM "table_41021" WHERE "Frequency" = '91.9 fm'