The first and the last critical frequencies (singularities) of a driving point impedance function of a passive network having two kinds of elements, are a pole and a zero respectively. The above property will be satisfied by
- $\text{RL}$ network only
- $\text{RC}$ network only
- $\text{LC}$ network only
- $\mathrm{RC}$ as well as $\mathrm{RL}$ networks