Which propagation method follows the earth's surface?

• A. Ground wave
• B. Direct wave
• C. Sky wave
• D. Space wave

Answer: (A)

The idea being tested is surface-bound propagation, where the radio wave travels close to and along the Earth's surface. Ground (surface) waves do exactly that: they hug the terrain, spreading along the surface by interacting with the ground’s conductivity and by diffraction around small obstacles. This makes them particularly useful at lower frequencies, where the signal can travel farther along the ground before attenuating.

In contrast, a direct (or space) wave goes in a straight line through the air from transmitter to receiver and over the horizon only if the path is clear. A sky wave relies on ionospheric reflection to reach distant receivers beyond the line-of-sight. The chosen option—the ground wave—fits the description of propagating along the Earth’s surface.