By performing cascading and/or summing/differencing operations using transfer function blocks G₁(s) and G₂(s), one CANNOT realize a transfer function of the form

Consider the following block diagram in the figure. The transfer function $$\frac{\mathrm C\left(\mathrm s\right)}{\mathrm R\left(\mathrm s\right)}$$ is

For the following system, When X₁(s) = 0 , the transfer function $$\frac{\mathrm Y\left(\mathrm s\right)}{{\mathrm X}_2\left(\mathrm s\right)}$$ is

The transfer function Y(s)/R(s) of the system shown is