Choose the letter A, B, C or D the word that has the underlined part different from others.

A. button

B. degree

C. socket

D. access

Tìm   ∫ ( cos ⁡ 6 x   -   cos ⁡ 4 x ) d x   l à :

A.  - 1 6 sin 6 x + 1 4 sin 4 x + C

B. 6 sin 6 x - 5 sin 4 x + C

C. 1 6 sin 6 x - 1 4 sin 4 x + C

D. - 6 sin 6 x + sin 4 x + C