Consider the square planar complex, MBrClPyNH3. Number of cis isomers possible for this complex is/are

Let a, b, c, d are monodentate ligands.Select any two ligands of your choice.Let us select a, bin (I), (II)    .   .   .   a and b are cis to each otherin (III)    .   .   .   a and b are trans to each other