Arithmetic mean describes the average trend of a group of data. It is the quotient of the sum of all data divided by the number of data. When using it in statistics, it should be noted that when extreme values, ambiguous data or heterogeneous data appear , Can not calculate the arithmetic mean. Based on the above definitions, Which of the following are suitable for calculating the arithmetic mean:. ['Statistics of the average age of residents in a community, including 204 children under 10 years old and 26 elderly people over 90 years old.', 'A company counts the average annual income of young employees under the age of 35 and finds that it is basically between 100,000 and 120,000 yuan. One of them is a company executive with an annual income of more than one million yuan.', 'Statistics on the average height of adolescents in a school, including all students in the preschool, primary and middle schools.', 'A city counts the average number of left-behind children in various districts and counties in the city. The districts and counties with a large number of migrant workers cannot perform accurate statistics, and only estimated data are provided.']