What was one of the ways that people of ancient times classified plants and animals?

by use
using a dichotomous key
using genetic analysis
by color

The right answer is by use.

Before the advent of genetics animals and plants were classified in the most simple and exploitable way, that is to say by use, for example the plants was classified in nutritive plants, phytotherapeutics (it even divided into subclasses) Toxic insect repellent ...

The correct answer is (a) by use

Earlier the people were not aware about the genetics and classification of plants and animals. So, they used to classify plants and animals by their use. The plants were used for many purposes such as eating, medicine, cosmetics. Either the plants were usable or non usable. Plants like neem, tulsi, ginger, turmeric were used as medicine.  Animals were used for obtained dairy products like milk and butter, for eating, for exacting colors out of them.