A system has a block G1(s) which has input x (s) and output y1(s). This output is fed as input to a second block G2(s) which has output y2(s). For this system, G1(s) = ( frac{s^{-1}}{1 + 2s^{-1} + s^{-2}} ).G2(s) for the given system to be invertible is given by _______________

• A. ( frac{s}{1+2s+s^2} )
• B. ( frac{1+2s+s^2}{s} )
• C. ( frac{1}{1+2s+s^2} )
• D. 1+2s+s²