The long-tail theory is a new theory emerging in the Internet age and was proposed by American Chris Anderson. The long-tail theory believes that in the past due to factors of cost and efficiency, people could only focus on important people or important things. If the normal distribution curve is used to describe these people or things, people can only pay attention to the "head" of the curve and will ignore most people or things that need more energy and cost to pay attention to in the "tail" of the curve. Which of the following cases, the long tail theory is used to emphasize the "tail". ['Although the "hot" economic power is not as good as it was then, we still pay absolute attention to it.', 'Businesses believe that listeners have an unlimited demand for non-popular music, and the market is extremely huge and should be paid attention to.', 'Vendors focus on 20% of mainstream products that 80% of customers buy, and focus on maintaining 20% of mainstream customers who buy 80% of their products.', 'When selling products, manufacturers focus on a few "VIP" customers, "no time" to take into account the majority of ordinary consumers.']