If `epsi_(0)` and `mu_(0)` are respectively, the electric permittivity and the magnetic permeability of free space, `epsi` and `mu` the corresponding quantities in a medium, the refractive index of the medium is
A. `sqrt((mu epsi)/(mu_(0) epsi_(0)))`
B. `(mu epsi)/(mu_(0) epsi_(0))`
C. `sqrt((mu_(0) epsi_(0))/(mu epsi))`
D. `sqrt((mu mu_(0))/(epsi epsi_(0)))`