Factors that can change in an experiment is called

Plz which of the following statements about life in europe during the middle ages is not accurate. a. by the middle ages the only unifying factor in europe was christianity. b. most people lived in rural areas and worked on farms. c. priest, monks and church officials were virtually the only people in europe who could read and write d. most people lived in cities or towns and worked as skilled artis most people lived in cities or towns and worked as skilled artisans.