question on listener interface

[Minu]

which interface must a class implement so that instances of the class are notified after any object is added to a session?
A. javax.servlet.http.HttpSessionListener
B. javax.servlet.http.HttpSessionValueListener
C. javax.servlet.http.HttpSessionBindingListener
D. javax.servlet.http.HttpSessionAttributeListener

the correct answer is D while i think it should be C.

Could somebody tell which is the correct answer and why?

[peppem]

In this post there is an example about the interfaces differences
http // w w w .coderanch.com/t/171721/Web-Component-Certification-SCWCD/HttpSessionBindingListener-HttpSessionAttributeListener

By reading this post and relative test, I think that both C, and D response are correct.