The friction head lost due to flow of a viscous fluid through a circular pipe of length L and diameter d with a velocity v and pipe Fanning friction factor f is

A

$$\frac{4fL}{d}.\frac{v^2}{2g}$$

B

$$\frac{4fL}{\pi d^2}.\frac{v^2}{2g}$$

C

$$\frac{v^2}{2g}$$

D

$$\frac{4fL}{\pi d}.\frac{v^2}{2g}$$