After the First World War, the effect of human and psychological factors became the main focus of organizational studies, which formed the second milestone of OB history. Most of the studies followed the footsteps of Taylor, and focused on efficiency of work activities. During 1925 to 1932, a series of studies known as Hawthorne Studies, conducted at Hawthorne Plant of the Western Electric Company; the studies at first was influenced from the scientific management principles, but developed to be the major research advancement in understanding of human behavior in organizations. The research at the Hawthorne Plant, which consisted of four separate studies that last over a seven-year period was directed by Fritz Roethlisberger; but Elton Mayo was the influential researcher who encouraged the organization’s management to further develop the Hawthorne studies which were preceded by a series of studies focusing on the effect of illumination conducted by himself in Philadelphia textile industry. The correct answer is Choice E.