Using the substitution u=sec(x), rewrite the integral ∫ tan⁷(x)sec(x)dx as an integral involving u. Which of the following options correctly represents the new integral?

A. ∫ u⁷ du
B. ∫ u⁶ du
C. ∫ u⁸ du
D. ∫ u⁵ du