Changying Li Shandong University   27 Shanda South Road School of Economics Shandong University Jinan, Shandong 250100 China   changyingli@sdu.edu.cn   http://www.econ.sdu.edu.cn/teacher/content.php?id=93           JEL Areas: L1 : Market Structure, Firm Strategy, and Market Performance: General D4 : Market Structure and Pricing: General