Answer:
C. taxonomy
Step-by-step explanation:
Approximately, there is around 8.7 million different types of organisms in the world. To create a proper classification for these organisms, The scientists took a look at each characteristics that can came based on their physical structures, environment where they live, their behaviors, the type of foods they consume , etc.
Even until today, scientists haven't be able to create a full taxonomy on all organisms that exist on the earth. There are a lot of areas that are extremely difficult to access , making the categorization almost impossible. (such as the ocean or dangerous part of rain forests)