Answer:
B. increase the amount of arable land
Terraces in agriculture are used for various purposes, but the most appropriate choice from the given options is:
**B. increase the amount of arable land**
Detailed explanation:
1. **Prevention of Soil Erosion:** Terracing involves creating step-like structures on sloped terrain. This helps in slowing down the flow of water, preventing soil erosion. As water moves down the slope, each terrace reduces its speed, allowing for better absorption by the soil.
2. **Arable Land Expansion:** By creating flat platforms on slopes, terracing effectively increases the amount of usable, arable land. This is crucial in areas with hilly or mountainous terrain where cultivating crops on slopes without terracing would be challenging.
3. **Water Conservation:** Terraces also help in water conservation. They capture and retain water, preventing it from quickly running off the slope. This allows the soil to absorb the water, benefiting crops and preventing downstream flooding.
4. **Crops Cultivation:** The level surfaces created by terracing provide suitable conditions for cultivating crops. This is especially important in regions with challenging topography, where terraces allow for the cultivation of crops that might otherwise be difficult to grow on steep slopes.
Option B, "increase the amount of arable land," encapsulates the primary purpose of using terraces in agriculture, making it the best answer from the provided choices.