Which of the following substitution is done in Bilinear transformations?

• A. s = ( frac{2}{T}[ frac{1+z^{-1}}{1-z^1}] )
• B. s = ( frac{2}{T}[ frac{1+z^{-1}}{1+}] )
• C. s = ( frac{2}{T}[ frac{1-z^{-1}}{1+z^{-1}}] )
• D. None of the mentioned