Is the subgroup H = {id, (12)(34), (13)(24), (14)(23)} a normal subgroup of S₄ ?
A) Yes, because it is a cyclic subgroup.
B) No, because it is not closed under conjugation.
C) Yes, because every subgroup of S₄ is normal.
D) No, because its elements do not commute with all elements of S₄ .