A reaction turbine stage has angles a, \[\alpha ,\]\[\beta ,\]\[\gamma \]as nozzle angle, inlet blade and outlet blade angle respectively. The expression for maximum efficiency of the turbine is given by:

• A. \[\frac{2{{\cos }^{2}}\beta }{1+{{\cos }^{2}}\beta }\]            
• B. \[\frac{2{{\cos }^{2}}\gamma }{1+{{\cos }^{2}}\gamma }\]
• C. \[\frac{2{{\cos }^{2}}\alpha }{1+{{\cos }^{2}}\alpha }\]                    
• D. \[\frac{\cos (\alpha +\beta )}{{{\cos }^{2}}\gamma }\]