When Congress establishes a new agency and the agency writes rules to perform its duties, these rules are identified as:

When Congress establishes a new agency, that agency is given the authority to create rules and regulations necessary to carry out its statutory mandate. These rules, formulated by the agency, are specifically categorized as administrative law. Administrative law governs the activities of governmental agencies and includes the rules and regulations they produce as they carry out their functions.

Statutory law refers to laws enacted by legislatures, which form the legal code. While the agency's enabling statute provides the legal framework for its operation, the specific rules created by the agency are applications of this framework and are thus classified as administrative law.

Common law, on the other hand, is based on judicial decisions and precedents rather than statutes or regulations. It evolves through the decisions made by judges in courts. Similarly, case law is a subset of common law and refers to the actual written opinions of the court in legal cases. Neither of these categories directly relates to the rules established by an administrative agency.

Thus, the distinction lies in the nature of the rules created by agencies, which are a fundamental component of administrative law, making it the correct choice in this context.