Which of the following relations is an equivalence relation?

(a) {(1, 1), (2, 2), (3, 3), (1, 2)}

(b) {(a, b) | (a = b) v (a is odd ^ b is even)}

(c) {(x, y) | x + y is even}

(d) {(t1, t2) | t1 and t2 are triangles, and some angle in t1 is equal to some angle in t2}

I know the answer is (c), but my question is how do you even work on (a) when it's just a list of points?