Netcom Solutions is an Internet Service Provider that has purchased a fresh wholesale bandwidth from network service provider GT&P$.$ Netcom Solutions has been using duplex technologies running through copper wires for its distribution. It now wants to upgrade to multiplexing technologies using fiber$-$optic cables so that it can allow multiple signals to travel simultaneously. Analyze which of the following types of multiplexing technologies Netcom should choose in this situation for its connection with GT&P so that it can operate with more channels.

a$.$ WDM

b$.$ FDM

c$.$ DWDM

d$.$ TDM