A physical quantity of the dimensions of length that can be formed out of $c, G,~\text{and}~\dfrac{e^2}{4\pi\varepsilon_0}$is [$c$ is the velocity of light, $G$ is the universal constant of gravitation and $e$ is charge]:
1. $c^2\left[G \dfrac{e^2}{4 \pi \varepsilon_0}\right]^{\dfrac{1}{2}}$
2. $\dfrac{1}{c^2}\left[\dfrac{e^2}{4 G \pi \varepsilon_0}\right]^{\dfrac{1}{2}}$
3. $\dfrac{1}{c} G \dfrac{e^2}{4 \pi \varepsilon_0}$
4. $\dfrac{1}{c^2}\left[G \dfrac{e^2}{4 \pi \varepsilon_0}\right]^{\dfrac{1}{2}}$

Planck's constant ($h$), speed of light in the vacuum ($c$), and Newton's gravitational constant ($G$) are the three fundamental constants. Which of the following combinations of these has the dimension of length?