The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary (K–T) extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago.
One reason is if someone is injured and needed to use pain pills, sometimes they get addicted to it
The answer is descent with modification.
Descent with modification practically means that a species have changed appearance wise over long periods of time to adapt to their environments better.
It is known as stimulus or the plural form stimuli. It can be external or internal.
