What is the relation between the exponents 'p', 'q', and 'r' in the function 'f(z) = z^p(z-3)^q(z+3)^r' to ensure that the only required branch cut is between -3 and 3 on the real axis?
a) p = q = r
b) p = -q = r
c) p = q = -r
d) p = -q = -r