Explanation: A unijunction transistor (UJT) is a three-terminal solid-state device used primarily in timing, oscillator, and trigger circuits due to its unique negative resistance characteristic. Its terminals are **Base 1 (B1)**, **Base 2 (B2)**, and an **Emitter (E)**. The UJT's structure consists of a bar of N-type semiconductor material with ohmic contacts at each end, forming Base 1 and Base 2. A P-type material is diffused into the N-type bar, creating a single PN junction that forms the Emitter. This single junction is what gives the device its "unijunction" name. * **B) Gate, cathode, and anode** are the terminals for a Silicon Controlled Rectifier (SCR) or other thyristors, not a UJT. * **C) Gate, base 1, and base 2** incorrectly includes "Gate," which is not a UJT terminal. "Gate" is typically found on Field-Effect Transistors (FETs) or SCRs. * **D) Gate, source, and sink** describes the terminals of a Field-Effect Transistor (FET) (though "sink" is usually called "drain"), not a UJT.