Histology is the study of:

• A. Muscles and their functions
• B. The skin, its structure, functions, diseases, and treatments
• C. The functions and activities performed by the body
• D. The microscopic anatomy of cells and tissues of plants and animals

Answer: (D)

Histology focuses on the microscopic anatomy of cells and tissues, studying how these tiny units are organized and how they relate to tissue function in plants and animals. This sets it apart from broader topics that look at body parts at a macroscopic level or at whole-body functions, and from fields that focus on a specific system like muscles or skin. So, the description that best fits is the microscopic anatomy of cells and tissues of plants and animals.