Concept:Each computer generation is identified by its main hardware technology; fifth-generation computers introduced ULSI microprocessors.Explanation:Vacuum tubes were used in first-generation computers.Integrated circuits were used in third-generation computers.VLSI microprocessors were used in fourth-generation computers.During the development of fifth-generation computers, ULSI microprocessors became the powerful new hardware technology used to support artificial intelligence and parallel processing.Answer:D. ULSI microprocessors.