For a LTI system consisting of two integrators, the output of the first integrator is inverted and fed as input to the sigma at beginning and output of the second integrator is also inverted and fed as input to the sigma at the beginning. The input is x (t) and output y (t), the transfer function is ______________

• A. ( frac{1}{s+4} )
• B. ( frac{1}{s^2+4s+3} )
• C. ( frac{1}{s^2-4s-3} )
• D. ( frac{1}{s^2-4s+3} )