When the backbone fiber is broken or the OLT cannot detect the expected optical signal (LOS) alarm, the possible cause is: (Multiple Choice)

When the backbone fiber is broken or the OLT cannot detect the expected optical signal (LOS) alarm, the possible cause is: (Multiple Choice)
A . There is a rogue ON U under the port
B . Port backbone fiber failure
C . All power off or failures under the port
D . The port laser is turned off

Answer: BCD