The following description of 1+1 and 1:1 optical line protection, the fault is (). (Multiple Choice)

The following description of 1+1 and 1:1 optical line protection, the fault is (). (Multiple Choice)
A . 1:1 optical line protection switching mode can only be double-ended switching
B . The main difference between 1:1 optical line protection and 1+1 optical line protection is whether the APS protocol is required.
C . 1+1 optical line protection and 1:1 optical line protection use the same protection board
D . According to different placement of OLP boards in the network, 1+1 optical line protection can be divided into 1+1 OMS path protection and 1+1 OTS path protection.

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Answer: BC