This is a discrete math question.

Let A = {1, 2, 3, 4} . Give an example of a non-empty binary relation on the set A that is:

(a) reflexive and symmetric, but not antisymmetric; (b) symmetric and antisymmetric, but not reflexive;

(c) transitive but neither symmetric nor antisymmetric; (d) antisymmetric but not transitive.