Concept:Development depends on both heredity and environment working together.
Explanation:Heredity provides inborn traits, instincts, and potential for growth.
Environment determines how those potentials are realized.
For example, heredity sets a range for IQ, while environment decides the exact score within that range.
Neither factor works alone.
All mental and social traits are shaped by environment, while inborn traits come from heredity.
Thus, developmental changes result from the unique interaction of genetic and environmental circumstances.
Answer:A. Unique combination of genetic and environmental circumstances.