A centrifugal pump running at 200 rpm and at its maximum efficiency is delivering a head of 30 m at a flow rate of 60 liters per min. If the speed of the pump is increased to 400 rpm, then head H is meters and flow rate Q in liters per min at maximum efficiency is

• A. H = 60, Q = 120
• B. H = 120, Q = 120
• C. H = 120, Q = 240
• D. H = 60, Q = 240