CREATE TABLE table_67337 ("Call sign" TEXT, "Frequency MHz" TEXT, "City of license" TEXT, "ERP W" FLOAT, "Class" TEXT, "FCC info" TEXT)

What is the name of call sign that uses a Frequency MHz of 91.1 fm?
SELECT "Call sign" FROM table_67337 WHERE "Frequency MHz" = '91.1 fm'
SELECT "Call sign" FROM "table_67337" WHERE "Frequency MHz" = '91.1 fm'