Which of the following mediums is capable of supporting high-frequency transmissions?

Optical fibers, coaxial cables, and waveguides are all capable of supporting high-frequency transmissions, making the choice of "All of the above" the correct answer.

Optical fibers use light to transmit data, which allows for extremely high frequencies and bandwidth capabilities. This medium is particularly advantageous for long-distance communication because it reduces signal loss and can transmit data at very high speeds, far beyond what is possible with electrical signals in traditional cables.

Coaxial cables can also handle relatively high-frequency signals, often used for cable television and internet transmission. The design of coaxial cables—with an inner conductor, outer conductor, and insulating material—helps to reduce electromagnetic interference, allowing for better performance at higher frequencies compared to other traditional electrical cables.

Waveguides, on the other hand, are specialized structures that guide electromagnetic waves, typically in the microwave range and higher. They are particularly effective for very high-frequency transmissions because they can carry waves without the losses commonly associated with other types of cables.

Therefore, each medium has the capability to support high-frequency transmissions, confirming that "All of the above" is indeed the correct answer.