Which of the following about system OSNR commissioning is wrong?

Which of the following about system OSNR commissioning is wrong?
A . Adjust the single-wave level first, and then adjust the optical power of the main line
B. One of the commissioning principles for OSNR flatness of the MPI-R point system: After the pump power is determined, use a spectrometer to detect the OSNR flatness of the MPI-R point. If the OSNR flatness does not meet the standard (OSNR flatness index ≤ 2dB), then need to adjust M40V
C. The multiplexer is an M40V single board, "look at the receiving end, adjust the sending end", in the case of ensuring that the optical power flatness meets the index requirements, the optical power flatness can be sacrificed to ensure the flatness of OSNR (or BER)
D. APE automatically adjusts the optical power of each channel to ensure that the optical power at the receiving end is flat, thereby ensuring the flatness of OSNR

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Answer: A