The refractive index of a certain glass is 1.5 for light whose wavelength in vacuum is 6000 $\text{Å}$. The wavelength of this light when it passes through glass is

• A

  $4000\text{Å}$

• B

  $6000\text{Å}$

• C

  $9000\text{Å}$

• D

  $15000\text{Å}$