Click the Exhibit button. When designing a DWDM system with multiple amplified spans， a pre-amp is needed at Site B to （）.

A. offset the OADM loss at site B
B. overcome the high multiplexer loss at site A
C. amplify signal levels after the high loss through Fiber Span 1
D. adjust add channels at site B to be at the same level as the passthrough channels
E. ensure that the per channel power is higher than the minimum needed for the post-amp at Site B