An ac source of variable frequency $\mathrm{f}$ is connected to an LCR series circuit. Which one of the graphs shown in Fig. represents the variation of current $\mathrm{l}$ in the circuit with frequency

When an $\mathrm{AC}$ source of emf $\mathrm{e}={\mathrm{E}}_0\sin 100\mathrm{t}$ is connected across a circuit, the phase-difference between the emf $\mathrm{e}$ and
the current $\mathrm{i}$ in the circuit is observed to be $\frac{\mathrm{\pi }}{4}$, as shown in Fig. If the circuit consists possibly only of $\mathrm{R}-\mathrm{C}$ or $\mathrm{R}$ $\mathrm{L}$ or $\mathrm{L}-\mathrm{C}$ in series, find the relationships between the two elements.