WAve length

The wavelengths of k_{\alpha } and k_{\gamma } X- Rays are \lambda _{1} and \lambda _{2 } respectively. The wavelength of L _{\beta } X- Rays is
A) \frac{\lambda _{1 } + \lambda _{2}}{2} B) \frac{\mid \lambda _{1 } - \lambda _{2}\mid }{2} C) \frac{ \lambda _{1 } \lambda _{2} }{\lambda _{1 } - \lambda _{2}} D) \frac{ \lambda _{1 } \lambda _{2} }{\lambda _{1 } + \lambda _{2}}