________blank is a high-frequency transmission medium that has a single solid-copper core.Multiple ChoiceTwisted pairCoaxial cableMicrowaveFiber-optic cable

The correct answer is Coaxial cable.

Coaxial cables are characterized by a single solid-copper core that is surrounded by an insulating layer and a braided copper shield, which allows for high-frequency transmission. This construction helps to minimize interference and allows for better data transmission compared to twisted pair cables, which use pairs of wires twisted together. Fiber-optic cable, on the other hand, transmits data using light rather than electrical signals, and microwaves are a type of electromagnetic radiation that is not a physical medium like the other options. Therefore, among the provided options, coaxial cable is the most accurate choice.