What planning considerations improve ground wave communications?

The correct answer emphasizes the significance of placing antennas at military crests, avoiding obstacles, and utilizing retransmission techniques to enhance ground wave communications.

Ground wave communication relies on the propagation of radio waves along the Earth's surface, and certain environmental and physical factors can greatly influence its effectiveness. By strategically positioning antennas at a military crest, which is the highest point in the area, the signals can operate more efficiently by maximizing their reach and minimizing interference from nearby obstacles, such as buildings or topography.

Obstacle avoidance is crucial because physical barriers can block or reflect signals, leading to degraded communication reliability. In scenarios where direct line-of-sight transmission is not achievable due to terrain or other obstructions, retransmission becomes vital. This involves using additional antennas or repeaters to relay the signal, thereby extending the communication range and improving clarity.

This option directly addresses the environmental variables and practical strategies necessary for successful ground wave communications, making it the most effective choice in this context.