**Ground Waves and Transmitters**

Ground waves are a type of electromagnetic wave that propagate along or near the Earth's surface. They are commonly used for communication purposes, particularly in the low-frequency range. When a transmitter sends out a ground wave, it propagates along the surface of the Earth and can travel a certain distance before its signal strength diminishes.

**Explanation of the Options**

a) Tilting: Tilting refers to the inclination or slanting of the ground wave propagation. However, tilting alone does not cause the disappearance of ground waves as one moves away from the transmitter. Tilting can affect the direction and coverage of the ground wave, but it does not directly result in their disappearance.

b) Maximum single-hop distance limitation: Maximum single-hop distance limitation refers to the maximum distance that a ground wave can travel in a single hop. However, this limitation does not cause the disappearance of ground waves. It only determines the maximum range of the ground wave before it needs to be propagated through other means, such as sky waves or space waves.

c) Interference from the sky waves: Sky waves are another type of electromagnetic wave that propagate upwards and bounce off the ionosphere, allowing long-distance communication. Interference from sky waves can affect the strength and quality of ground waves, but it does not directly cause their disappearance. Ground waves can still propagate even in the presence of sky waves, although their effectiveness may be reduced.

d) Loss of line-of-sight condition: Line-of-sight refers to the unobstructed path between the transmitter and receiver. In the case of ground waves, a direct line-of-sight is not necessary for propagation. Ground waves can travel along or near the Earth's surface, even if there are obstacles in the path. Therefore, the loss of line-of-sight condition does not cause the disappearance of ground waves.

**Explanation of Option A**

The correct answer is option 'A' - tilting. Tilting of the ground wave propagation refers to the inclination or slanting of the wave as it travels along the Earth's surface. As one moves away from the transmitter, the ground wave propagates over a larger distance, and the wavefronts start to tilt or become more inclined. This tilting causes the energy of the ground wave to spread out in different directions, resulting in a decrease in signal strength. Eventually, as the distance increases, the tilting becomes more significant, and the ground wave's energy dissipates, leading to its disappearance.

In summary, as one moves away from the transmitter, the ground waves eventually disappear due to the tilting of the wavefronts, which causes the energy to spread out and diminish.