(f(x) = ax + b/cx + d), where (a), (b), (c), and (d) are positive and (a ⋅ d) is not equal to (b ⋅ c). Which of (a/b), (a/c), and (a/d) cannot be in the domain of (f⁻¹)?
a) (a/b)
b) (a/c)
c) (a/d)
d) None of the above