Mr Maths

Pick the true statements

a) Every cycle is a permutation
b) Every permutation is a cycle
c) Every transposition is a cycle
d) Every transposition is a permutation

Let R be a ring. Which of the followings are subrings of R?

a) {x€R | ax=0} for a€R

b) {x€R | ax=0 or xa=0} for a€R

c) {x€R | xa=ax for all a€R}.