Which of the following layers is situated directly above the D layer in the ionosphere?

The layer situated directly above the D layer in the ionosphere is the E layer. The ionosphere is divided into several layers, and understanding their arrangement is crucial for grasping how radio wave propagation works.

The D layer, located at a lower altitude, is primarily responsible for absorbing low-frequency radio waves during the day. Directly above this is the E layer, which plays a significant role in reflecting radio waves at higher frequencies, particularly during the day when ionization levels are optimal. The F layer is actually situated above the E layer and exists at higher altitudes, allowing for more substantial ionization and reflection of radio frequencies, especially during nighttime.

In summary, the correct layer directly above the D layer is the E layer, as it is part of the ionosphere's structure and determines radio wave behavior and communication effectiveness.