The relationship between e, S and na is ______

• A. (n_a=e* frac{1+S}{1+e} )
• B. (n_a=e* frac{1-S}{1-e} )
• C. (n_a= frac{1-S}{1+e} )
• D. (n_a=e* frac{1-S}{1+e} )