You create Microsoft Windows-based applications. You design a composite user control that is used to enter e-mail addresses. The control is as shown in the following exhibit. (Refer to the Exhibit.) The control validates the user input by using a regular expression. The control validates e-mail addresses and prevents the user from submitting blocked e-mail addresses. The control must permit the user to correct the entry if the user enters a blocked e-mail address. You need to provide feedback if the user enters a blocked e-mail address in the txtEmailAddress text box. What should you do?
A.
Write a code segment to throw an application exception.
B.
Set a custom property of the composite user control to indicate a data validation error.
C.
Write a code segment to display a message box if the user enters a blocked e-mail address.
D.
Write a code segment to clear the txtEmailAddress text box if the user enters a blocked e-mail address.