Tìm \(\int {\left( {\cos 6x - \cos 4x} \right)dx} \) là:

A. \(\frac{1}{6}\sin 6x - \frac{1}{4}\sin 4x + C\)

B. \(6\sin 6x - 4\sin 4x + C\)

C. \( - \frac{1}{6}\sin 6x + \frac{1}{4}\sin 4x + C\)

D. \( - 6\sin 6x + \sin 4x + C\)