CREATE TABLE table_66918 ("Colt model no." TEXT, "Name" TEXT, "Stock" TEXT, "Fire control" TEXT, "Rear sight" TEXT, "Forward assist" TEXT, "Case deflector" TEXT, "Barrel length" TEXT, "Barrel profile" TEXT, "Barrel twist" TEXT, "Hand guards" TEXT, "Bayonet Lug" TEXT, "Muzzle device" TEXT)

Name the hand guards for ar-15a2 government carbine and barrel twist of 1:9
SELECT "Hand guards" FROM table_66918 WHERE "Name" = 'ar-15a2 government carbine' AND "Barrel twist" = '1:9'
SELECT "Hand guards" FROM "table_66918" WHERE "Barrel twist" = '1:9' AND "Name" = 'ar-15a2 government carbine'