Design a circuit that converts a four-bit Gray code a, b, c, d to a four-bit binary number w, x, y, z.

a. w=ab'c x=(a xor d) y=(x xor c) z=(b xor d)

b. w=a x=(a xor b) y=(x xor c) z=(y xor d)

c. w=ab'cd x=a'b'cd' y=(x xor c) z=ab

d. w=a xor c x=(a xor d) y=(x xor c) z=(w xor d)