You are developing an ASP.NET Web page that uses jQuery validation. The user should enter a valid email address in a text box that has ID txtEmail. The page must display "E-Mail address required" when the user does not enter an address and "Invalid e-mailaddress" when the user enters an address that is not formatted properly. You need to ensure that the appropriate error message is displayed when the text box does not contain a valid e-mail address.   Which two code segments should you add？（）

• A、
• B、
• C、
• D、