The correct order of the complexes ${\left[ {{\rm{Co}}{{\left( {{\rm{N}}{{\rm{H}}_3}} \right)}_5}\left( {{{\rm{H}}_2}{\rm{O}}} \right)} \right]^{3 + }}({\rm{A}}),{\left[ {{\rm{Co}}{{\left( {{\rm{N}}{{\rm{H}}_3}} \right)}_6}} \right]^{3 + }}({\rm{B}}),{\left[ {{\rm{Co}}{{({\rm{CN}})}_6}} \right]^{3 - }}({\rm{C}})$ and ${\left[ {{\rm{CoCl}}{{\left( {{\rm{N}}{{\rm{H}}_3}} \right)}_5}} \right]^{2 + }}({\rm{D}})$ in terms of wavelength of light absorbed is