多项选择题 Which three technologies are used to reduce chromatic dispersion accumulation in fiber-optic transmission systems? （）(Choose three.)

单项选择题 What is the phenomenon called where different wavelengths of light travel at different speeds?（）

单项选择题 A 2.5 Gb/s (OC-48 or STM-16) optical signal with a dispersion tolerance of 1200 ps/nm goes through fiber with 18ps/nm*km of dispersion. How many 15216-DCU-350 equivalents are needed for enough compensation after traveling 100 km?（）