**Explanation:**

The best alignment for a canal is when it is aligned along the ridge line. This means that the canal is constructed along the highest point of the land, following the natural alignment of the ridge. There are several reasons why aligning a canal along the ridge line is the best option.

**1. Water flow:**

Aligning a canal along the ridge line ensures that the water flow is maximized. Since the ridge line is the highest point of the land, gravity helps the water to flow naturally and efficiently along the canal. This reduces the need for additional pumping and ensures a constant and consistent water flow.

**2. Stability:**

The ridge line is usually the most stable part of the land. It is less susceptible to erosion and soil instability compared to other parts of the terrain. By aligning the canal along the ridge line, the risk of canal failure due to soil erosion and instability is minimized.

**3. Cost-effective:**

Aligning a canal along the ridge line is cost-effective in terms of construction and maintenance. Construction costs are reduced because the natural alignment of the ridge line eliminates the need for extensive excavation and leveling of the land. Maintenance costs are also reduced as the stability of the ridge line reduces the likelihood of costly repairs and maintenance work.

**4. Land utilization:**

Aligning the canal along the ridge line allows for better land utilization. The land on either side of the canal can still be used for various purposes such as agriculture, residential areas, or infrastructure development. By utilizing the ridge line for the canal, valuable land is not wasted and can be used for other productive purposes.

**Conclusion:**

In conclusion, aligning a canal along the ridge line is the best option due to its advantages in terms of water flow, stability, cost-effectiveness, and land utilization. This alignment ensures efficient water flow, reduces the risk of canal failure, saves construction and maintenance costs, and allows for optimal land utilization. Therefore, option 'B' is the correct answer.