Explanation: A TRIAC is a three-terminal semiconductor device that functions as a bidirectional AC switch. Its three terminals are the Gate, Anode 1 (A1 or Main Terminal 1, MT1), and Anode 2 (A2 or Main Terminal 2, MT2). The Gate terminal controls when the TRIAC turns on, typically by applying a small current pulse. Once triggered, current can flow in either direction between Anode 1 and Anode 2, allowing the TRIAC to switch AC power. Options A (Emitter, base 1, and base 2) describes a Unijunction Transistor (UJT). Option B (Base, emitter, and collector) describes a Bipolar Junction Transistor (BJT). Option C (Gate, source, and sink) is incorrect; while "gate" and "source" are FET terminals, "sink" is not a standard terminal name (it should be "drain").