You create a Microsoft ASP.NET application by using the Microsoft .NET Framework version 3.5.  You create a Web form in the application by using the following code fragment. （Line numbers are included for reference only.） You plan to create a client-side script code by using ASP.NET AJAX.  You need to ensure that while a request is being processed， any subsequent Click events on the btnSubmit Button control are suppressed.  Which code fragment should you insert at line 10？（）

• A、A
• B、B
• C、C
• D、D