Taxonomy (is an unnecessary science) (helps to classify the immense diversity of life) (is only used by some scientists) (is the study of animal behavior) IT CAN BE MORE THAN ONE ANSWER

Explanation:

1. The classification and naming of organisms in an ordered system that is intended to indicate natural relationships, especially evolutionary relationships.

2. The science, laws, or principles of classification.

3. An ordered arrangement of groups or categories

b.have there own function.