Which of the following devices can route electrical signals only when activated by an external control signal？（）

A.Gather information from the customer.
B.Isolate the problem on the device.
C.Read the service documentation for possible causes.
D.Check the parts life counters.

A.Explain the issues of the call， the steps taken to resolve them and query the client if they have any additional needs.
B.Explain the solution to the issue and then provide the client with the technicians contact information in case they have any questions.
C.Give the client a technical explanation on the issue and how it was fixed； throw any faulty equipment in the clients garbage.
D.Proceed to the next service call， check back with the client in a week to see if they have any additional needs.

A.after two unplanned service calls.
B.according to manufacturers specifications.
C.when the device is becoming unreliable.
D.every sixty days.