Final answer:
The Belmont Report is the foundational document of the U.S. system of protection for human subjects in research, focusing on principles of respect, beneficence, and justice.
Step-by-step explanation:
The document that forms the foundation of the U.S. national system of human subjects' protection is the Belmont Report. Options such as the Nuremberg Code and the Declaration of Helsinki have significantly influenced the development of ethical guidelines for the protection of human subjects in research. However, it is the Belmont Report that set forth the basic ethical principles specific to the conduct of biomedical and behavioral research involving human subjects in the United States. These principles include respect for persons, beneficence, and justice. The Belmont Report underpins the formulation of regulations in the U.S. that govern institutions and researchers via Institutional Review Boards (IRBs) to ensure the protection of participants in clinical trials and other human subjects research.