Complete answers or none, and please read question:

Find (if it were possible) the Most General Unifier (MGU) of:

(a) (a) {P(f(x), z), P(y, a)};

(b) {P(f(x), a), P(y, f(w))};

(c) {P(a, x, f(g(y))), P(b, h(z,w), f(w))};

(d) {S(x, y, z), S(u, g(v, v), v)};