Social medicine refers to the study of the medical problems related to the population's life, old age, disease, and death from a social perspective. It studies the comprehensive role played by social factors in the different stages of life preparation, protection, and improvement of quality of life. Management provides a theoretical basis for formulating corresponding health goals, policies, strategies and measures to ensure the health of the population. According to the above definitions, which of the following is not in the scope of social medical research? ['The medical and health department provides free treatment for Li who has cancer.', 'Investigation of disease prevention and health care of left-behind children by medical and health departments.', 'The health department develops a plan for occupational disease census, prevention and control.', 'Medical and health departments implement a "four frees and one care" policy for people living with HIV.']