多项选择题
A. low optical power
B. high optical power
C. few optical channels
D. many optical channels
E. low chromatic dispersion
F. high chromatic dispersion
G. too much power differential in the optical channels
单项选择题 Why are the 1300 nm and 1550 nm regions of the fiber spectrum primarily used for optical communications?（）
单项选择题 What is an advantage of an externally modulated laser over a directly modulated laser?（）
单项选择题 What is the difference between the transmitted power and the sensitivity of the receiver?（）