Hall believed that each individual in his or her lifetime reenacted all of the evolutionary stages of the human species. what is this idea called?

The correct answer is: Recapitulation Theory.

Explanation:

The Recapitulation Theory began as an idea by Étienne Serres in the 1820s that later, in 1886, was took by Ernst Haekel when he proposed his "Ontogeny recapitulates phylogeny" theory. Recapitulation Theory combines evolution and embryology and states that the development of an individual when an embryo, summarizes the evolutionary history of its species.

not too sure but maybe in the hot springs.

b) the inside picture would look at a very high temperature in a very low ph