Đạo hàm của hàm số\[y = {\cot ^2}\left( {\cos x} \right) + \sqrt {\sin x - \frac{\pi }{2}} \]là
A. \[y' = - 2\cot \left( {\cos x} \right)\frac{1}{{{{\sin }^2}\left( {\cos x} \right)}} + \frac{{\cos x}}{{2\sqrt {\sin x - \frac{\pi }{2}} }}.\]
B. \[y' = 2\cot \left( {\cos x} \right)\frac{1}{{{{\sin }^2}\left( {\cos x} \right)}}.\sin x + \frac{{\cos x}}{{2\sqrt {\sin x - \frac{\pi }{2}} }}.\]
C. \[y' = - 2\cot \left( {\cos x} \right)\frac{1}{{{{\sin }^2}\left( {\cos x} \right)}} + \frac{{\cos x}}{{\sqrt {\sin x - \frac{\pi }{2}} }}.\]
D. \[y' = 2\cot \left( {\cos x} \right)\frac{1}{{{{\sin }^2}\left( {\cos x} \right)}}.\sin x + \frac{{\cos x}}{{\sqrt {\sin x - \frac{\pi }{2}} }}.\]