CREATE TABLE table_75604 ("Call sign" TEXT, "Frequency MHz" FLOAT, "City of license" TEXT, "ERP W" FLOAT, "Class" TEXT, "FCC info" TEXT)

Class of d, and a Frequency MHz smaller than 107.7, and a ERP W smaller than 232 has what call sign?
SELECT "Call sign" FROM table_75604 WHERE "Class" = 'd' AND "Frequency MHz" < '107.7' AND "ERP W" < '232'
SELECT "Call sign" FROM "table_75604" WHERE "Class" = 'd' AND "ERP W" < '232' AND "Frequency MHz" < '107.7'