Which of the Following Does NOT Exemplify a Natural Experiment

Which of the following does NOT exemplify a natural experiment?

A) exploring the behavioral consequences on families when the breadwinner is killed on the job
B) doing a comparative analysis of families that choose to stay and those who choose to move out of an ethnically changing neighborhood to find out the underlying causes for the difference in their choices
C) determining the effects of the preferential hiring of people with disabilities on the morale of people without disabilities
D) comparing the results of standardized test scores after the school year
E) recruiting participants to watch a documentary and then measuring their opinions