The dimensional formula of a physical quantity represented by $\frac{e^2}{4 \pi \varepsilon_0 \hbar}$ is (where $e$ is the charge of an electron,$\varepsilon_0$ is the permittivity of free space,and $\hbar$ is the reduced Planck's constant). Note: The expression $\frac{e^2}{4 \pi \varepsilon_0 \hbar}$ is equivalent to the fine-structure constant $\alpha$ multiplied by the speed of light $c$.

• A
  $[M^1 L^1 T^{-1}]$
• B
  $[L^1 T^{-1}]$
• C
  $[M^1 L^0 T^{-1}]$
• D
  $[M^1 L^1 T^{-2}]$