Which one of the following octahedral complexes will not show geometrical isomerism (A and B are monodentate ligands)?

• A

  $\left[{\mathrm{MA}}_5\mathrm{B}\right]$

• B

  $\left[{\mathrm{MA}}_2{\mathrm{B}}_4\right]$

• C

  $\left[{\mathrm{MA}}_3{\mathrm{B}}_3\right]$

• D

  $\left[{\mathrm{MA}}_4{\mathrm{B}}_2\right]$