The correct choice is (a) integer exponents
Explanation: Exponentiation with integer exponents is termed in any multiplicative monoid. Exponentiation is described inductively by 1) h^0 = 1 for all h ∈ S, h^n+1 = h^n h and non-negative integers n, If n is a negative integer then h^n is only defined if h has an inverse in S. Monoids define many structures including groups and rings (under multiplication).