Can enterprises selectively purchase social security? For example, they only buy medical care, not old-age insurance.

Enterprises cannot selectively purchase social security.

People's Republic of China (PRC) social insurance law

Article 2 The state establishes social insurance systems such as basic old-age insurance, basic medical insurance, industrial injury insurance, unemployment insurance and maternity insurance, so as to guarantee citizens' right to receive material assistance from the state and society in accordance with the law in case of old age, illness, industrial injury, unemployment and maternity.

Article 3 The social insurance system adheres to the principles of wide coverage, basic protection, multi-level and sustainability, and the level of social insurance should be compatible with the level of economic and social development.

Article 4 Employers and individuals who pay social insurance premiums according to law in People's Republic of China (PRC) have the right to inquire about payment records and personal rights and interests records, and ask social insurance agencies to provide social insurance consultation and other related services.

Individuals enjoy social insurance benefits according to law and have the right to supervise the payment of their own units.

Article 58 An employing unit shall, within 30 days from the date of employment, apply to the social insurance agency for social insurance registration for its employees. If the social insurance has not been registered, the social insurance agency shall verify the social insurance premium it should pay.

Employees-free individual industrial and commercial households who voluntarily participate in social insurance, part-time employees who do not participate in social insurance in the employing unit and other flexible employees shall apply to the social insurance agency for social insurance registration.

The state establishes a national unified personal social security number. Personal social security number is a citizen's identity number.

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.