Chọn mệnh đề đúng: cosx khác 1 <=> x khác pi/2 + k pi

A. $\cos x\ne 1\iff x\ne \frac{\pi }{2}+k\pi \left(k\in Z\right)$

B. $\cos x\ne 0\iff x\ne \frac{\pi }{2}+k\pi \left(k\in Z\right)$

C. $\cos x\ne -1\iff x\ne -\frac{\pi }{2}+k2\pi \left(k\in Z\right)$

D. $\cos x\ne 0\iff x\ne \frac{\pi }{2}+k2\pi \left(k\in Z\right)$