Why do scientists who study evolution think of 20 million years as a short time?

the endomembrane system i think

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms

the correct answer is: " ventricles " .

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