Concept:Farmers' income depends on farm output, so anything that suddenly reduces output makes income unstable.
Explanation:Diseases and pests attack crops and farm animals, reducing yields or destroying whole harvests.
These attacks are often sudden and unpredictable, causing heavy losses for farmers.
Because most Nigerian farmers depend on agriculture, such losses make their income vary sharply from season to season.
Industrial pollution, mining, and population growth are not the major direct causes of unstable farm income in Nigeria.
Answer:A. the effect of diseases and pests