Giá trị của cos [pi/3 + (2k + 1)pi] là

A. $\cos [\frac{\mathrm{\pi }}{3}+(2k+1\left)\mathrm{\pi }\right]=-\frac{\sqrt{3}}{2}$

B. $\cos [\frac{\mathrm{\pi }}{3}+(2k+1\left)\mathrm{\pi }\right]=\frac{1}{2}$

C. $\cos [\frac{\mathrm{\pi }}{3}+(2k+1\left)\mathrm{\pi }\right]=-\frac{1}{2}$

D. $\cos [\frac{\mathrm{\pi }}{3}+(2k+1\left)\mathrm{\pi }\right]=\frac{\sqrt{3}}{2}$