Correct Option: B. Light Explanation of Why the Answer is Correct: When considering the distribution of cattle in West Africa, several environmental and biological factors come into play. These factors include pastures, diseases, and rainfall, all of which significantly influence where cattle can thrive. However, light, while important for plant growth, does not directly influence the distribution of cattle in the same way that the other factors do.

1. Pastures: Cattle require adequate grazing land to feed on. The availability of nutritious pastures is crucial for their growth and milk production. Regions with rich, fertile soils that support lush grasslands are more likely to have higher cattle populations. Therefore, pastures are a primary factor influencing cattle distribution.
2. Diseases: The prevalence of diseases such as trypanosomiasis (sleeping sickness) and other cattle diseases can severely limit where cattle can be raised. Areas with high disease incidence may see lower cattle populations due to higher mortality rates and reduced productivity. Thus, diseases are a significant factor in determining where cattle can be successfully raised.
3. Rainfall: Rainfall directly affects the availability of water and the growth of pastures. Regions with adequate rainfall support lush vegetation, which is essential for grazing. Conversely, areas with low rainfall may experience droughts, leading to poor pasture conditions and insufficient water supply for cattle. Therefore, rainfall is a critical factor influencing cattle distribution.
4. Light: While light is essential for photosynthesis and plant growth, it is not a direct factor in the distribution of cattle. Most regions in West Africa receive sufficient sunlight for plant growth, and thus, light does not vary significantly enough across the region to impact where cattle can be raised. The other factors (pastures, diseases, and rainfall) have a more pronounced effect on cattle distribution.

Explanation of Why the Other Options Are Wrong or Weaker:

• A. Pastures: This option is incorrect because pastures are one of the most significant factors influencing cattle distribution. Without adequate grazing land, cattle cannot thrive.
• C. Diseases: This option is also incorrect as diseases are a major limiting factor for cattle populations. Areas with high disease prevalence will see reduced cattle numbers due to health issues.
• D. Rainfall: This option is incorrect because rainfall is crucial for maintaining the health of pastures and providing water for cattle. Regions with sufficient rainfall support larger cattle populations.

Summary of Key Points:

• Pastures are essential for cattle feeding and growth, making them a primary factor in distribution.
• Diseases can limit cattle populations due to health risks and mortality, significantly affecting where cattle can be raised.
• Rainfall is critical for pasture growth and water availability, influencing cattle distribution.
• Light does not significantly affect cattle distribution in West Africa, making it the correct answer to the question.

This understanding of the factors influencing cattle distribution is vital for anyone studying agricultural science, particularly in the context of livestock management in West Africa.