CREATE TABLE table_21720 ("Class" TEXT, "Part 1" TEXT, "Part 2" TEXT, "Part 3" TEXT, "Part 4" TEXT, "Verb meaning" TEXT)

What class is the verb wich its part 4 is frosinn
SELECT "Class" FROM table_21720 WHERE "Part 4" = 'frosinn'
SELECT "Class" FROM "table_21720" WHERE "Part 4" = 'frosinn'