Final answer:
The term for special rules made by an appropriate authority for waterways linked to high seas is called International rules, as defined by international law and key documents like the UNCLOS.
Step-by-step explanation:
The term that refers to special rules made by an appropriate authority for waterways connected with the high seas and navigable by seagoing vessels is d) International rules. These rules are part of international law, which is a set of formal and informal rules that loosely govern the international system, including aspects such as maritime law. The United Nations Convention on the Law of the Sea (UNCLOS) is a key document in this regard, clarifying numerous maritime issues such as boundaries, fishing rights, and shipping lanes.
International law plays a crucial role by setting expectations of behavior and facilitating interactions in common areas like the sea. The UN Convention on the Law of the Sea has been instrumental in establishing these rules, which are recognized and enforced by various countries around the globe.