For the block diagram shown in the figure, the correct expression for the transfer function $G_{d}=\frac{y_{1}(s)}{d(s)}$ is
- $\frac{-G_{p 1} G_{c 2}}{\left(1+G_{c 1} G_{c 2} G_{p 1}\right)\left(1+G_{c 2} G_{p 2}\right)}$
- $\frac{-G_{p 1} G_{c 2}}{1+G_{c 2} G_{p 2}+G_{c 1} G_{c 2} G_{p 1} G_{p 2}}$
- $\frac{-G_{p 1} G_{c 2}}{1+G_{c 2} G_{p 2}+G_{c 1} G_{c 2} G_{p 1}}$
- $\frac{1}{1+G_{c 2} G_{p 2}+G_{c 1} G_{c 2} G_{p 1} G_{p 2}}$