Step 1: Coaxial Cable Transmission.
The transmission of high frequencies in coaxial cables is influenced by both the dielectric properties of the materials and the skin effect, which causes higher frequencies to propagate along the surface of the conductor.
Step 2: Conclusion.
Therefore, the correct answer is option (D).
Final Answer:
\[
\boxed{\text{(D) the dielectric and skin effect}}
\]