If z=a+biz = a + biz=a+bi, which expression represents the square of its modulus ∣z∣2|z|^2∣z∣2?
a2+b2a^2 + b^2a2+b2
a2−b2a^2 - b^2a2−b2
a+ba + ba+b
z2z^2z2