Development mechanism of producer services industry for metropolises 并列题名：Development mechanism of producer services industry for metropolises Development trend of producer services industry and China's option Research on the mechanism of producer service industry for the strategic emerging industry 并列题名：Development trend of producer services industry and China's option Research on Co-agglomeration mechanism of producer service industry and its spatial effect On producer services industry in megalopolis 并列题名：On producer services industry in megalopolis The development of producer service industry