Wavelength division multiplexing is a technique for carrying multiple fiber$-$optic signals on a single network medium. There are several types of this multiplexing technique, including Coarse Wavelength Division Multiplexing $($CWDM$).$ Dense Wavelength Division Multiplexing $($DWDM$),$ and Bidirectional Wavelength Division Multiplexing $($BWDM$,$ or just WDM$).$ Which of the following is one of the ways in which these types of multiplexing differ?They carry different numbers of channels on a single medium.They use different wavelength spacings.They provide different amounts of signal amplification.They use different forms of amplitude modulation,