Calculate the roots of the polynomial p(z) = z⁴ - 4 and use them to factor p(z) into a product of quadratics that have real coefficients.

a) (z² - 2)(z² + 2)
b) (z + 2)(z + √2)(z - √2)(z - 2)
c) (z² - 4)(z² + 4)
d) (z - 2)(z + 2)(z² + 4)