In order to maintain the reach of a typical 100G WAN transport system(~1500 km)，several system improvements have to be made to recover the lost（1）,including the use of low-loss low-nonlinearity（2），Raman amplification,and stronger error correction.
(1)
A.noise   
B.SNR   
C.speed   
D. eeor
(2)
A.optical fiber   
B.traffic   
C.internet   
D.signaling