In a gating system design, a down sprue of 180 mm length has a diameter of 20 mm at its top end. The liquid metal in the pouring cup is maintained up to 60 mm height. The diameter (in mm) of the down sprue at its lower end to avoid aspiration will be:

• A. 11.11
• B. 14.14
• C. 25
• D. 17.32