The unit speed of the turbine runner is

• A. <img src="/_files/images/mechanical-engineering/hydraulic-machines/197-74-1.png">
• B. <img src="/_files/images/mechanical-engineering/hydraulic-machines/197-74-2.png">
• C. <img src="/_files/images/mechanical-engineering/hydraulic-machines/197-74-3.png">
• D. <img src="/_files/images/mechanical-engineering/hydraulic-machines/197-74-4.png">