In a circuit L, C, and R are connected in series with an alternating voltage source of frequency f. The current leads the voltage by 45°. The value of  C is 

• A

  $\frac{1}{2\mathrm{\pi f}(2\mathrm{\pi fL}+\mathrm{R})}$

• B

  $\frac{1}{\mathrm{\pi f}(2\mathrm{\pi fL}+\mathrm{R})}$

• C

  $\frac{1}{2\mathrm{\pi f}(2\mathrm{\pi fL}-\mathrm{R})}$

• D

  $\frac{1}{\mathrm{\pi f}(2\mathrm{\pi fL}-\mathrm{R})}$