What happened soon after settled groups started to thrive?

What would lead a historian to consider two events to have a relationship of correlation rather than causation

Who did the first work in creating vaccines

Which of the following accurately describes the workforces of the united states and canada? a. most of the workforce in the united states and canada is employed in the service industry. b. most of the workforce in the united states and canada is employed in the educational field. c. most of the workforce in the united states and canada is employed in manufacturing and mining. d. most of the workforce in the united states and canada is employed in agriculture.