What is an example of internal stimuli?

What did hunter gathers do to alter the environment?

The embryos of a bird, a reptile, and a mammal are similar in appearance. how does comparing the physical appearance of embryos of different species support the theory of evolution? a. it shows that these organisms share a common ancestor. b. it provides evidence that these organisms eat the same foods.c. it shows that these organisms share the same habitat.d. it provides evidence that these organisms suffered a genetic mutation.

The changes that the students observed, rapid breathing and sweating, would be classified as a to a change in a system.