In a circular pipe of length L and diameter d, a viscous liquid is flowing with a velocity v. The loss in head, is

• A. <img src="/_files/images/civil-engineering/hydraulics/150-7.113-1.png">
• B. <img src="/_files/images/civil-engineering/hydraulics/150-7.113-2.png">
• C. <img src="/_files/images/civil-engineering/hydraulics/150-7.113-4.png">
• D. <img src="/_files/images/civil-engineering/hydraulics/150-7.113-3.png">
• E. none of these.