Ash Grove Cement Company hired Electric Company of Omaha (ECO) to relocate a cable tray. ECO gained access to the tray from the flat roof of Ash Grove's building and controlled the work. While walking backwards and carrying cable, Darryl Didier, an employee of ECO, fell twenty feet of the roof, onto a concrete surface. He wants to file for a lawsuit to recover the damages he suffered. Which company Darryl should sue? Explain your answer through references to the duties and liabilities of principals and agents.