Evaluate values in dropdownlist C#

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C#

Hello Everyone

I have 3 dropdownlist : ddl,ddl2,ddl3.
It contains values like ddl1 :A1,A2,A3
ddl2:B1,B2,B3
ddl3:C1,C2,C3

I want the user to select values as A1,B1,C1.
In case if the user selects A1,B1,C3 it should display an error stating the user should select A1,B1,C1 before any other combinations.

Do any one have solutions for this.
I want this to be done using c#.

What I have tried:

Could not find anything related to the above condition.
Tried to combine the solutions here and there
but could not succeed.





Not found any solutions.