What CAR tool feature would the administrator use?

An administrator wants to see how long a specific IP phone extension is in use during a given period of time. What CAR tool feature would the administrator use?
A. System Reports > Traffic > Summary by Phone Number
B. CDR > Search > By Call Precedence Level
C. Device Reports > Route Patterns/Hunt Groups > Route and Line Group Utilization
D. User Reports > Top N > By Duration