$\frac{d}{d x}\left[\log \tan \left(\frac{\pi}{4}+\frac{x}{2}\right)\right]=?$

$\sec \frac{x}{2}$

$2 \sec x$

$\sec x$

$\sec x \tan x$

$\frac{1}{2} \sec \left(\frac{\pi}{4}+\frac{x}{2}\right)$