CREATE TABLE table_21715 ("Class" TEXT, "Part 1" TEXT, "Part 2" TEXT, "Part 3" TEXT, "Part 4" TEXT, "Verb meaning" TEXT, "Usual PIE origin" TEXT)

For part 2 *lauk, what is listed for part 4?
SELECT "Part 4" FROM table_21715 WHERE "Part 2" = '*lauk'
SELECT "Part 4" FROM "table_21715" WHERE "Part 2" = '*lauk'