The . . . . . . . . validator is used to display all of the validation error messages in a single location on aWeb page.

The correct answer is: D. ValidationSummary

A ValidationSummary is a server control that displays all of the validation error messages in a single location on a Web page. It is used to improve the usability of a Web page by grouping all of the validation error messages together in one place.

The other options are incorrect because:

• A CompareValidator is a server control that compares the value of a control to a specified value or range of values.
• A RangeValidator is a server control that validates that the value of a control is within a specified range of values.
• A RequiredFieldValidator is a server control that validates that a control has a value.

I hope this helps! Let me know if you have any other questions.