In the cascade amplifier shown in the given figure, if the common - emitter stage $\left(Q_{1}\right)$ has a transconductance $\mathrm{gm}_{1}$, and the common base stage $\left(Q_{2}\right)$ has a transconductance $\mathrm{gm}_{2^{\prime}}$, then the overall transconductance $g\left(=i_{0} / v_{1}\right)$ of the cascade amplifier is
- $g_{m 1}$
- $g_{m 2}$
- $\frac{g_{m 1}}{2}$
- $\frac{g_{m 2}}{2}$