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

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

• B

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

• C

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

• D

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