What was the basis of classification for animals according to Aristotle?

Presence of red blood

The correct answer is Option (4): Presence of red blood

Aristotle divided animals into two main groups based on whether they possessed red blood or not. He classified animals into those with red blood (which includes most vertebrates) and those without red blood (which includes mainly invertebrates like insects, mollusks, etc.).

This classification was a fundamental and observable trait used by Aristotle to distinguish between different groups of animals, primarily focusing on a physiological characteristic like the color of blood. This categorization was an early attempt to classify animals based on a visible and distinctive feature that was commonly observable at that time.