The terminal velocity (v) of a sphere of radius r and specific weight W, which travels vertically downwards in a liquid of viscosity and specific weight W, is

• A. <img src="/_files/images/civil-engineering/hydraulics/157-7.214-1.png">
• B. <img src="/_files/images/civil-engineering/hydraulics/157-7.214-2.png">
• C. <img src="/_files/images/civil-engineering/hydraulics/157-7.214-3.png">
• D. <img src="/_files/images/civil-engineering/hydraulics/157-7.214-4.png">