When single board services such as LOA/TOA/THA/TOM/TOG are activated, the local client-side interface reports an L_SYNC alarm. What is the reason?

When single board services such as LOA/TOA/THA/TOM/TOG are activated, the local client-side interface reports an L_SYNC alarm. What is the reason?
A . The local client-side interface receives light abnormally, and the opposite client-side interface receives light abnormally.
B . The local client-side interface receives light normally and the opposite client-side interface receives light abnormally.
C . The local client-side interface receives light normally, and the opposite client-side interface receives light normally.
D . The local client-side interface receives light abnormally, and the opposite client-side interface receives light normally.

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Answer: D