d
\(\text { Here, } R_{C}=2 \mathrm{k} \Omega=2000 \Omega, V_{0}=4 \mathrm{V}\)

\(\alpha=100, R_{B}=1 \mathrm{k} \Omega=1000 \Omega, V_{i}=?\)

Voltage gain, \(A=\beta \frac{R_{C}}{R_{B}}=100 \times \frac{2000}{1000}=200\)

\( \text { Also, } A =\frac{V_{0}}{V_{i}} \text { or } V_{i}=\frac{V_{0}}{A}=\frac{4}{200} \)

\(=\frac{2}{100} \mathrm{V}=20 \mathrm{mV}\)