Hello,
I have a form with 4 dropdown list, that 3 of the dependent dropdown list show same options like that:

Degree :(Bachelor, Master, PhD)
Priority Major 1: (Major1, Major2, Major3)
Priority Major 2: (Major1, Major2, Major3)
Priority Major 3: (Major1, Major2, Major3)

How can show an error when a same item selected.

Thank you for your help.