What technology does a cable modem primarily operate over?

A cable modem primarily operates over coaxial cable television lines, which is why the correct choice is C. This technology is designed to utilize the existing infrastructure of cable TV networks to provide high-speed internet access to users. The cable modem communicates with the service provider's modem that is typically located at the headend of the cable system.

Coaxial cables can carry a large amount of data, which is essential for internet service that requires high bandwidth for activities such as streaming, gaming, and downloading large files. This also allows for a shared bandwidth system, where multiple users can connect to the internet simultaneously without significant degradation of service.

In contrast, the other options represent different technologies not associated with cable modems. Fiber optic lines are used for fiber-optic internet services, DSL connections utilize telephone lines for data communication, and satellite links provide internet access via satellites, often with higher latency and lower speeds compared to cable connections.