To replace a pipe of diameter D by n parallel pipes of diameter d, the formula is

• A. <img src="/_files/images/civil-engineering/hydraulics/153-7.164-1.png">
• B. <img src="/_files/images/civil-engineering/hydraulics/153-7.164-2.png">
• C. <img src="/_files/images/civil-engineering/hydraulics/153-7.164-3.png">
• D. <img src="/_files/images/civil-engineering/hydraulics/153-7.164-4.png">
• E. <img src="/_files/images/civil-engineering/hydraulics/153-7.164-5.png">