If You Are Asked a Question to Which You Don't

If you are asked a question to which you don't know the answer,the proper response should be:

A) "I'm afraid I will not be able to answer your queries."
B) "Shall we keep the questions toward the end of the session?"
C) "I don't know the answer but I will research it and get back to you"
D) "This seems to digress from the topic in discussion."
E) "Questioners should ensure that they benefit the entire audience."