A physical quantity of the dimensions of length that can be formed out of $c, G$ and $\frac{e^2}{4\pi {\epsilon }_0}$, where [$c$ is velocity of light, $G$ is universal constant of gravitation, $e$ is charge & ${\epsilon }_0$ is permittivity of free space]:

• Correct answer
  A

  $\frac{1}{c^2}{\left[G\frac{e^2}{4\pi {\epsilon }_0}\right]}^{\frac{1}{2}}$
• B

  $c^2{\left[G\frac{e^2}{4\pi {\epsilon }_0}\right]}^{\frac{1}{2}}$
• C

  $\frac{1}{c^2}{\left[\frac{e^2}{G4\pi {\epsilon }_0}\right]}^{\frac{1}{2}}$
• D

  $\frac{1}{c}G\frac{e^2}{4\pi {\epsilon }_0}$

Hence, the correct answer is option: 'A'.