Which of the following is the correct expression for internal efficiency in steam turbines?

• A. ( frac{Heat , converted , into , useful , work}{Total , adiabatic , heat , drop} )
• B. ( frac{Net , work , done , on , shaft , per , stage , per , kg , of , steam}{Adiabatic , heat , drop , per , stage} )
• C.
• D. ( frac{Net , work , done , on , shaft , per , stage , per , kg , of , steam}{Total , adiabatic , heat , drop} )
• E. ( frac{Heat , converted , into , useful , work}{Net , work , done , on , shaft , per , stage , per , kg , of , steam} )