Changes that reduce the efficiency of organ systems refers to a. chronological aging b. biological aging c. psychological aging d. social aging

The question pertains to the types of aging and how they affect organ systems. Let's analyze the options given.

1. Chronological Aging: This refers to the actual time that has passed since a person was born. It’s a measure of time and doesn’t directly relate to the efficiency of organ systems.

2. Biological Aging: This is concerned with the physiological changes that occur in the body over time, affecting the functions of organs and systems. It is the most relevant option as it focuses on the physical decline that can lead to reduced efficiency.

3. Psychological Aging: This refers to changes in mental processes, cognition, and emotional states with age. While important, it doesn’t directly correlate with organ system efficiency.

4. Social Aging: This is about the changing roles and relationships as one ages, which impacts social interactions and community involvement rather than organ systems.

Final Answer

The correct answer is b. biological aging as it directly refers to changes that reduce the efficiency of organ systems.