An amplifier without feedback has a voltage gain of $50$, input resistance of $1 \mathrm{~K} \Omega$ and output resistance of $2.5 \mathrm{~K} \Omega$. The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedback factor of $0.2$ is
- $1 / 11 \mathrm{~K} \Omega$
- $1 / 5 \mathrm{~K} \Omega$
- $5 \mathrm{~K} \Omega$
- $11 \mathrm{~K} \Omega$