The following is about the system OSNR commissioning error:

The following is about the system OSNR commissioning error:
A . Adjust single-wave flatness first, and then adjust the main line optical power
B . One of the measurement principle of the MPI-R point system OSNR flatness: After the pump power is determined, test the OSNR flatness of the MPI-R point by a spectrometer detector, if the OSNR flatness is not to up standard (OSNR flatness index ≤ 2dB), then Need to adjust M40
D . The multiplexer is an M40V single board, "looking at the receiving end and debugging the transmitting end". When the optical power flatness meets the requirements of the index, the optical power flatness can be sacrificed to ensure the OSNR (or BER) flatness
E . APE automatically adjusts the optical power of each channel to ensure that the optical power at the receiving end is flat, thereby ensuring the flat of OSNR

Answer: A