In which of the following cases can we expect a joint ion effect?

a) We add a little KCl solution to a saturated solution with silver chloride

b) We add some NH₄Cl solution to a saturated solution of CdCO₃

c) We add a little iron (III) bromide solution to a saturated solution of AgBr

d) We add some magnesium nitrate solution to a saturated solution of PbSO₄