Developmental Psychology studies the changes that occur from infancy to old age. It focuses on understanding how individuals develop physically, cognitively, and emotionally over their lifespan. This field of psychology takes into account various factors that contribute to development, including genetic, biological, environmental, and social influences.

Here is a detailed explanation of why Developmental Psychology is the correct answer:

1. Definition of Developmental Psychology:
Developmental Psychology is a branch of psychology that examines and explains the changes individuals experience throughout their lifespan. It seeks to understand how individuals develop physically, cognitively, and emotionally from infancy to old age.

2. Focus on Lifespan Development:
One of the main features of Developmental Psychology is its emphasis on studying the entire lifespan. It examines the changes that occur from birth until death, allowing researchers to gain a comprehensive understanding of human development.

3. Physical Development:
Developmental Psychology investigates how individuals' bodies change and mature over time. It explores the physical growth, motor skills, and changes in the body's structure and function from infancy to old age. This includes studying puberty, aging, and the impact of genetics on physical development.

4. Cognitive Development:
Another area of focus in Developmental Psychology is cognitive development. It explores how individuals' thinking, problem-solving abilities, language skills, and memory change and develop throughout their lives. This includes studying the development of intelligence, perception, attention, and other cognitive processes.

5. Emotional and Social Development:
Developmental Psychology also examines emotional and social development. It investigates how individuals' emotions, social skills, relationships, and identity develop and change over time. This includes studying the formation of attachments, peer relationships, moral development, and the impact of family and culture on emotional and social development.

6. Factors Influencing Development:
Developmental Psychology takes into account various factors that influence development. These include genetic factors, biological processes, environmental factors (such as parenting styles and socioeconomic status), and social factors (such as cultural norms and peer influence). By considering these factors, researchers can gain a more comprehensive understanding of how individuals develop.

In conclusion, Developmental Psychology is the branch of psychology that studies the changes that occur from infancy to old age. It examines physical, cognitive, emotional, and social development and considers various factors that influence development. By studying these changes, researchers can gain valuable insights into human growth and behavior across the lifespan.