A plane electromagnetic wave in a free space is represented by an equation.

A. $${\Delta ^2}\overrightarrow E - \mu { \in _0}\frac{{{\partial ^2}\overrightarrow B }}{{\partial {t^2}}} = 0$$

B. $${\Delta ^2}\overrightarrow E - {\mu _0}{ \in _0}\frac{{{\partial ^2}\overrightarrow B }}{{\partial {t^2}}} = 0$$

C. $${\Delta ^2}\overrightarrow E - {\mu _0}{ \in _0}\frac{{{\partial ^2}\overrightarrow E }}{{\partial {t^2}}} = 0$$

D. $${\Delta ^2}\overrightarrow E - \mu \sigma \frac{{{\partial ^2}\overrightarrow E }}{{\partial t}} + \mu \in \frac{{{\partial ^2}\overrightarrow E }}{{\partial {t^2}}} = 0$$

Answer: Option C