During which stage of the demographic transition shown above does a population begin to experience an explosive increase in growth?

Stage 2                                        

Explanation:

Demographic transition: The term "demographic transition" is described as a model that is based on the interpretation of Warren Thompson during 1929 and is described as a model to explain "population change" over a period in time.

Stage 2 of the "demographic transition" is distinguished as a rapid decrease in a specific country's "death rate" whereas the "birth rate" remains high. Therefore, the total population associated with a specific country in "stage 2" would increase due to "births outnumber deaths" yet not due to the rising birth rate.

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.