Why is it important to leave some residual dispersion at an amplifier site when 10Gb/s signals in a DWDM system have gone through a dispersion compensating device?

A.
Reduces the effect of polarization mode dispersion

B.
Avoids gain tilt through the amplifier

C.
Compensating to zero dispersion has too much loss penalty

D.
Suppresses some non-linear effects like XPM and SPM

E.
None of the above