What are AT LEAST 3 examples of health milestones which may have led to a significant decrease in the human population

Ahusband who believed that his wife was having an affair with his brother hired an arsonist to burn down the brother's house. they planned for the husband to take his brother to a ballgame so that the arsonist would be able to set the house on fire without detection. after the husband and brother left for the ballgame, however, the arsonist decided to abandon the plan and immediately left town without doing anything further. when the husband returned from the ballgame with the brother, he saw the house still standing and blurted out what was supposed to have happened. the husband and the arsonist were arrested and charged with conspiracy to commit arson. at the arsonist's trial, his attorney argued that he was innocent of the conspiracy because he decided not to go ahead with the plan, and nothing criminal had in fact occurred.at common law, how should a jury find the arsonist? a not guilty of conspiracy, because going to a ballgame is not a criminal overt act.b not guilty of conspiracy, because the husband, not the arsonist, committed the overt act.c guilty, because the husband executed his part of the plan.d guilty, because the arsonist agreed to set the brother's house on fire.