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Selected Control(s) Validation
Single Require Field Validator can be used to validated selected control(s). Use ControlsToValidate property to validated selected list of controls only.
<KSingle Required Field Validator is here >
<cc1:KSingleRequiredFieldValidator ControlTypesToValidate="" ControlsToValidate="TextBox1,ListBox1" ID="KSingleRequiredFieldValidator2" runat="server"></cc1:KSingleRequiredFieldValidator >

Text Box  
Drop Downlist
List Box