单项选择题 Given the formula: (Fiber Attenuation * Km) + (Splice Attenuation * # of Splices) + (Connector Attenuation * # of Connectors) + (Optical Fiber or OADM) + Buffer(Fiber aging)) With regard to SONET/SDH optical calculations, what will the given formula provide?（）

多项选择题 What three in combination are factors that can cause four-wave mixing in fiber-optic cables? （）(Choose three.)

单项选择题 Why are the 1300 nm and 1550 nm regions of the fiber spectrum primarily used for optical communications?（）