If the closed-loop transfer function $T(s)$ of a unity negative feedback system is given by
\[
\mathrm{T}(\mathrm{s})=\frac{a_{n -1} \mathrm{~s}+a_{n}}{\mathrm{~s}^{n}+n_{1} s^{n-1}+\ldots+a_{n-1} s+a_{n}}
\]
then the steady state error for a unit ramp input is
- $\frac{a_{n}}{a_{n-1}}$
- $\frac{a_{n}}{a_{n-2}}$
- $\frac{a_{n-2}}{a_{n-2}}$
- zero