Consider the definite integral: ∫(sin(x) / cos²(x)) dx. The most appropriate substitution to simplify this integral is u = cos(x), where after making this substitution and simplifying (using trig identities), we obtain the integral:

a) ∫(1 / u²) du
b) ∫(1 / u) du
c) ∫(1 / u³) du
d) ∫(1 / u⁴) du