The correct answer is A. Histology.
Histology is the study of tissues, which are groups of cells that are similar in structure and function. Tissues are the basic building blocks of organs, which are the structures that carry out the functions of the body.
Anatomy is the study of the structure of the body, including the organs and tissues. It is a branch of biology that deals with the form and structure of organisms and their parts.
Ecology is the study of the relationships between organisms and their environment. It is a branch of biology that deals with the interactions between organisms and their physical and biological surroundings.
Taxonomy is the science of classifying organisms. It is a branch of biology that deals with the naming and classification of organisms.
In conclusion, the correct answer is A. Histology. Histology is the study of tissues, which are groups of cells that are similar in structure and function. Tissues are the basic building blocks of organs, which are the structures that carry out the functions of the body.