If the function f(x) is defined as 5sec(5x), what is the derivative of f(x)?
A) f'(x) = 5sec(5x)
B) f'(x) = 5sec(5x)tan(5x)
C) f'(x) = 5sec²(5x)
D) f'(x) = 25sec(5x)tan(5x)