Which of the following equations is electromagnetic wave equation?

• A. \(∇^2 E ̅-\frac{σ}{μ}\frac{ (∂E ̅)}{∂t}-\frac{μ}{ϵ} \frac{ (∂^2 E ̅)}{(∂t^2 )}=0\)
• B. \(∇^2 E ̅-{σ}{ϵμ}\frac{ (∂E ̅)}{∂t}-\frac{μ}{σ} \frac{ (∂^2 E ̅)}{(∂t^2 )}=0\)
• C. \(∇^2 E ̅-\frac{ϵ}{μ}\frac{ (∂E ̅)}{∂t}-\frac{μ}{\sigma} \frac{ (∂^2 E ̅)}{(∂t^2 )}=0\)
• D. \(∇^2 E ̅-{σ}{μ}\frac{ (∂E ̅)}{∂t}-{μ}{ϵ} \frac{ (∂^2 E ̅)}{(∂t^2 )}=0\)