You need to ensure that the extender can be user toextend only text boxes and that the targetID property can reference only buttons

You are developing an ASP.NET AJAX extender control.
The extender includes the following segment.
public class DisabledButtonExtender : ExtenderControlBase
{
[ExtenderControlProperty]
public string TargetID
{
get{…}
set{…}
}
}
You need to ensure that the extender can be user toextend only text boxes and that the targetID property can
reference only buttons.
What should you do?

A.
Apply the following attribute to the class.
[ValidationProperty(“TextBox”)]
Apply the fallowing attribute to TargetID
[Filterable(true)]

B.
Apply the following attribute to the class.
[TargetControlType(typeof(TextBox))]
Apply the following attribute to TargetID
[Filterable(true)]

C.
Apply the following attribute to the class.
[ValidationProperty(“TextBox”)]
Apply the following attribute to TargetID
[IDReferenceProperty(typeof(Button))]

D.
Apply the following attribute to the class.
[TargetControlType(typeof(TextBox))]
Apply the following attribute to TargetID
[IDReferenceProperty(typeof(Button))]

Explanation:
[TargetControlType(typeof(TextBox))]
public class DisabledButtonExtender : ExtenderControlBase
{
[ExtenderControlProperty]
[DefaultValue(“”)]
[IDReferenceProperty(typeof(Button))]
http://www.asp.net/web-forms/tutorials/ajax-control-toolkit/getting-started/creating-a-custom-ajax-control-toolkitcontrol-extender-cs