If ${\mathrm{AB}}_4$ molecules is a polar molecule, a possible geometry of ${\mathrm{AB}}_4$ is:

If the given molecule is polar, then it does not have symmetrical geometry because dipole moment can't be canceled out. When  ${\mathrm{AB}}_4$ molecule is present in square pyramidal structure, it will have dipole moment. The other three structures do not have dipole moment because of symmetry.