Write the given trigonometric function in terms of $\cos x$.
$\tan x$

• A. $\pm \frac{\sqrt{1+{\cos }^{2}x}}{\cos x}$
• B. $\pm \frac{\sqrt{{\cos }^{2}x-1}}{\cos x}$
• C. $\pm \frac{\sqrt{1-{\cos }^{2}x}}{1+{\cos }^{2}x}$
• D. $\pm \frac{\sqrt{1-{\cos }^{2}x}}{\cos x}$

Answer: (D)