The correct answer is: A. CompareValidator
A CompareValidator is a server-side control that validates the contents of a control against a constant value or the property stored in another control. It is used to ensure that the value entered by the user is within a specified range or matches a specified value.
The RangeValidator is used to validate that a value is within a specified range. The RequiredFieldValidator is used to validate that a field is not empty. The ValidationSummary is used to display a list of all validation errors on a page.
Here is an example of how to use a CompareValidator:
<asp:CompareValidator ID="CompareValidator1" runat="server" ControlToValidate="TextBox1" ErrorMessage="The value in TextBox1 must be greater than 10." Operator="GreaterThan" Value="10" />
In this example, the CompareValidator will validate that the value entered in TextBox1 is greater than 10. If the value is not greater than 10, an error message will be displayed.