Which of the following statements are true?
I.    The set of all odd integers is a monoid under multiplication.
II.   The set of all complex number is a group under multiplication
III.  The set of all integers under the operation * given by a * b = a+b-ab is a monoid
IV.   Zs under symmetric difference   defined by A B = (A-B) ∪ (B-A) is an abelian group