For a positive integer n, let U(n) = {r̅ ∈ Zn ∶ gcd(r, n) = 1} be the group under multiplication modulo n. Then, which one of the following statements is TRUE?
1
U(5) is isomorphic to U(8)
2
U(10) is isomorphic to U(12)
3
U(8) is isomorphic to U(10)
4
U(8) is isomorphic to U(12)