A、It is based on knowledge level. B、It is based on cognitive level. C、It is random. D、It is controversial. C

Primary or elementary education is the first years of formal, structured education that occurs during childhood. In most Western countries, it is compulsory for children to receive primary education.
    Primary education generally begins when children are four to seven years of age. (16) The division between primary and secondary education is somewhat arbitrary, but it generally occurs at about twelve years of age. Some educational systems have separate middle schools for that period. Primary and secondary education together are sometimes, in particular, in Canada and the United States, referred to as "K-12" education.
    Typically, primary education is provided in schools. The child will stay, in steadily advancing classes, until they complete it and move on to secondary schooling. Children are usually placed in classes with one teacher who will be primarily responsible for their education and welfare for that year. This teacher may be assisted to varying degrees by some teachers in certain subject areas, often music or physical education. (17) The continuity with a single teacher and the opportunity to build up a close relationship with the class is a notable feature of the primary education system. Over the past few decades, schools have been testing various arrangements which break from the one-teacher, one-class pattern.
    The major goals of primary education are establishing foundations in science, geography, history and other social sciences. (18) The relative priority of various areas, and the methods used to teach them, are an area of considerable political debate.
Questions 16 to 18 are based on the passage you have just heard.
16. What can we learn about the division between primary and secondary education?
17. What is an important feature of the primary education system?
18. What is an area of political dispute over primary education?