A particle of mass m is suspended from the ceiling through a string of length L. The particle moves in a horizontal circle of radius r . The speed of the particle is 

• A

  $\frac{\mathrm{rg}}{\sqrt{{\mathrm{L}}^2-{\mathrm{r}}^2}}$

• B

  $\frac{\mathrm{r}\sqrt{\mathrm{g}}}{{\left({\mathrm{L}}^2-{\mathrm{r}}^2\right)}^{\frac{1}{4}}}$

• C

  $\frac{\mathrm{r}\sqrt{\mathrm{g}}}{{\left({\mathrm{L}}^2-{\mathrm{r}}^2\right)}^{\frac{1}{2}}}$

• D

  $\frac{\mathrm{mgL}}{{\left({\mathrm{L}}^2-{\mathrm{r}}^2\right)}^{\frac{1}{2}}}$