After a Key Service Unit (KSU) phone system is installed, the technician tests the system by taking line one off the hook and calling the home from a cell phone. Instead of line two ringing the installer receives a busy signal. The BEST troubleshooting step would be to:

A.
review the incoming call programming in the phone system.

B.
review the wiring for the central office lines into the phone system.

C.
review rollover settings with the phone company.

D.
review the voice mail system programming.