Malaria thrives in humid conditions favoring mosquito breeding

Steps:

• Identify malaria as a disease transmitted by Anopheles mosquitoes, which require standing water for breeding.
• Recognize that humidity affects mosquito survival and reproduction rates.
• Compare areas: Higher humidity in R supports more mosquitoes, increasing infection proportion.
• Eliminate unrelated factors like population density or sewage, which don't directly influence malaria vectors.

Why A is correct:

• Mosquitoes breed in stagnant water, and higher humidity in R prevents evaporation, creating ideal conditions for larvae development per vector biology principles.

Why the others are wrong:

• B: Proximity to equator correlates with warmth but not directly with humidity or breeding sites.
• C: Higher population increases total cases but not the proportion (prevalence rate) without vector influence.
• D: Sewage relates to bacterial diseases like cholera, not mosquito-borne malaria.

Final answer: A