The circuit in figure employs positive feedback and is intended to generate sinusoidal oscillation. If at a frequency $f_{0}, \mathrm{~B}(f)=\Delta \frac{V_{f}(f)}{V_{0}(f)}=\frac{1}{6} \angle 0^{\circ}$, then to sustain oscillation at this frequency
- $\mathrm{R}_{2}=5 \mathrm{R}_{1}$
- $\mathrm{R}_{2}=6 \mathrm{R}_{1}$
- $\text{R}_{2}=\frac{\text{R}_{1}}{6}$
- $\mathrm{R}_{2}=\frac{\mathrm{R}_{1}}{5}$