Introduction:
Irrigation canals are man-made channels designed to distribute water for agricultural purposes. The alignment of these canals plays a crucial role in ensuring efficient water distribution and minimizing losses. The correct answer to the question is option 'A', which states that irrigation canals are generally aligned on a ridge line. Let's delve into the reasoning behind this alignment.

Explanation:
1. Ridge line alignment:
The alignment of irrigation canals along a ridge line is the preferred choice for several reasons:

- Gravity flow: Aligning canals along a ridge line takes advantage of the natural slope or gradient of the land. Gravity allows water to flow freely downhill, minimizing the need for additional energy input such as pumps. This ensures a continuous and efficient flow of water throughout the irrigation system.

- Uniform distribution: Ridge line alignment helps in achieving uniform distribution of water. As the canals follow the contours of the land, the water can be evenly distributed to different fields or plots. This ensures that all crops receive an adequate amount of water for their growth and development.

- Reduced erosion: Ridge line alignment helps in minimizing soil erosion. When canals are aligned along the ridge line, the water flow is controlled, preventing excessive erosion of the soil. This is particularly important in hilly or sloping terrains where erosion can be a major concern.

- Optimal land use: Aligning canals along the ridge line allows for optimal land use. Since the canals follow the contours of the land, the land between the canals can be efficiently utilized for cultivation. This maximizes the agricultural potential of the area and reduces the wastage of land.

- Cost-effective: Ridge line alignment is cost-effective as it requires less excavation and construction work compared to other alignment options. This reduces the overall cost of the irrigation project while maintaining its effectiveness.

Conclusion:
In conclusion, irrigation canals are generally aligned on a ridge line due to various advantages such as gravity flow, uniform water distribution, reduced erosion, optimal land use, and cost-effectiveness. This alignment ensures efficient water distribution and contributes to the overall success of agricultural practices in the area.