For viscous flow between two parallel plates, the pressure drop per unit length is equal to

A

$$12 \frac{\mu \overline{U} L}{egD^{2}}$$

B

$$12 \frac{\mu \overline{U} }{D^{2}}$$

C

$$12 \frac{\mu \overline{U}L}{D^{2}}$$

D

$$32 \frac{\mu \overline{U} L}{D^{2}}$$