What two situations prevent the supervisor from silently monitoring the phone conversation of an agent in IPCC Express Enhanced?（）

• A、The agent is logged in and is on the phone. 
• B、The agent is logged in but is not on the phone. 
• C、The supervisor is a participant in a phone call. 
• D、The supervisor is not a participant in a phone call. 
• E、The supervisor has barged in.