Final answer:
The 100BaseFX standard is most commonly used with a fiber-optic network backbone due to its suitability for use with fiber-optic cables, offering faster speeds and longer distances compared to traditional copper cables.
Step-by-step explanation:
The 1000BaseCX, 100BaseT, 100BaseFX, and 100BaseTX standards are all related to Ethernet network technologies, but they differ in their signalling and cabling requirements. When we discuss a fiber-optic network backbone, we're usually referring to the infrastructure with the highest speed and longest reach within a network.
The correct answer among the options provided is c. 100BaseFX. 100BaseFX is an Ethernet standard for fiber-optic cable, and provides faster speeds and longer distances compared to traditional copper cables like those used in 100BaseT (which includes 100BaseTX) and 1000BaseCX configurations. This makes 100BaseFX a common choice for fiber-optic backbones, especially in networks that predate the more modern 1000Base and 10Gbe fiber standards.