Normally distributed demand curve. The protruding part in the middle is the "head". The relatively flat part on both sides is called the "tail". Most of the demand is concentrated in the "head" part. The distribution in the "tail" is personalized and small. The long-tail effect means that all the markets distributed in the "tail" will add up to a market larger than the "head" market, emphasizing "personalization" and "small profit large market", that is, only Make very little money for everyone, but make a lot of money for everyone. The root refers to the above definition. Which of the following are the long tail effects:. ['Many people do n’t choose gifts. Xiao Ren has established a website for choosing gifts. According to the requirements of different customers, he chooses corresponding gifts and charges a service fee of 5 yuan per month. After half a year, the monthly income exceeds 100,000 yuan.', "The trend of young people's online shopping is intensifying. Lao Zhao's clothing store business is gradually declining, and he switched to operating fresh products supermarkets. After half a year, the monthly profit exceeds the original clothing store.", 'Xiaogao opened an online store in 2010, mainly selling sports shoes. In 2017, he began to help friends sell cheap and local souvenirs in mountainous areas. In 2018, the sales of souvenirs exceeded that of sports shoes.', "Xiao Di runs an art training school with sufficient students. At the request of the majority of parents six months ago, children's English training was added. At present, the income of English training exceeds that of art."]