In X-ray spectrum, transition of an electron from an outer shell to an inner shell gives a characteristics X-ray spectral line. If we consider the spectral lines ${\mathrm{K}}_{\mathrm{\beta }},{\mathrm{L}}_{\mathrm{\beta }} \mathrm{and} {\mathrm{M}}_{\mathrm{\alpha }}$  , then   

• A

  ${\mathrm{K}}_{\mathrm{\beta }},{\mathrm{L}}_{\mathrm{\beta }}$ and have a common inner shell  

• B

  ${\mathrm{K}}_{\mathrm{\beta }},{\mathrm{L}}_{\mathrm{\beta }}$and have a common outer shell

• C

  ${\mathrm{L}}_{\mathrm{\beta }},{\mathrm{M}}_{\mathrm{\alpha }}$ and have a common outer shell

• D

  ${\mathrm{L}}_{\mathrm{\beta }},{\mathrm{M}}_{\mathrm{\alpha }}$ and have a common inner shell