What are two important considerations when using 2- or 4-channel 15216 OADMs？（）

A.All Add channels require uniform power levels.

B.The flexibility of wavelengths per OADM is limited.

C.It is easier to balance Pass-Through and Add channels.

D.There is lower pass-through loss using multi-channel OADMs.

E.You can extract a single channel without dropping other channels.