题目

Group buying is one of the fastest growing trends in South Africa today. Industry leaders are confident that the growth potential remains strong since group buying is location-specific(区域性的). Start-up costs are low and profit room remains high, so many sites continue to receive invested money despite widespread criticism and Facebook’s decision to phase out of the deals business due to privacy concerns. In the early stages of all industries, some companies fail because they cannot compete with stronger companies in difficult economic conditions. To deal with difficult conditi请设计实验证明在高度相同时，斜面越长越省力．