Which component should you log from the Lync Server Logging Tool?

Your network contains a Lync Server 2010 server named Server1.
A user named User1 reports that he is unable to sign in to Server1.
You verify that User1 can connect to the network and that other users can sign in to Server1.
You need to identify why User1 cannot sign in to Server1.
Which component should you log from the Lync Server Logging Tool?

A.
AD Connect

B.
Server Agent

C.
SIP Stack

D.
User Services

Explanation:
http://social.technet.microsoft.com/Forums/en-GB/ocsclients/thread/abcc18be-8da8-4603-a536-11235b57999b

http://207.46.16.248/en-us/library/gg437266.aspx