Jill, a technician, is installing several PCs in a home that is pre-wired with Ethernet to seven rooms. In the wiring closet all the Ethernet cables are hanging free and are not labeled. Which of the following tools would the technician use to locate the cable that runs to each room?（）

• A、Extension magnet
• B、Toner probe
• C、Multimeter
• D、Optical Time Domain Reflectometer (OTDR)