In Chezy's formula V = C rs for calculating the velocity of flow in circular sewer of diameter D running full, the value of hydraulic mean radius is

• A. <i>D</i>
• B. <img src="/_files/images/civil-engineering/waste-water-engineering/181-9.29-1.png">
• C. <img src="/_files/images/civil-engineering/waste-water-engineering/181-9.29-2.png">
• D. <img src="/_files/images/civil-engineering/waste-water-engineering/181-9.29-3.png">
• E. <img src="/_files/images/civil-engineering/waste-water-engineering/181-9.29-4.png">