The detention time of a circular tank of diameter d and water depth H, for receiving the sewage Q per hour, is

• A. <img src="/_files/images/civil-engineering/waste-water-engineering/190-9.173-1.png">
• B. <img src="/_files/images/civil-engineering/waste-water-engineering/190-9.173-2.png">
• C. <img src="/_files/images/civil-engineering/waste-water-engineering/190-9.173-3.png">
• D. <img src="/_files/images/civil-engineering/waste-water-engineering/190-9.173-4.png">