Estimating the size of government is difficult for a variety of reasons. Which of the following is NOT one of them? a) Government meshes with the private and nonprofit sectors to produce and provide many public goods. b) Our system of intergovernmental relations has lower levels of government carrying out federal programs and purposes. c) Government activity like regulatory activities (e.g., OSHA, EPA, etc.) that are highly impactful but budgetarily insignificant. d) All of the above. They are all reasons why estimating the size of government is difficult.