What are the three terminals of a silicon controlled rectifier (SCR)?

A Silicon Controlled Rectifier (SCR) is a four-layer solid-state device that controls current flow. Because it acts essentially as a switchable diode, it shares the standard diode terminals: the anode and the cathode. The third terminal is the gate, which is used to trigger the device into its conducting state. By applying a small voltage to the gate, the SCR allows a much larger current to flow from the anode to the cathode. The other options describe completely different types of semiconductor devices. "Base, collector, and emitter" are the terminals of a Bipolar Junction Transistor (BJT). "Gate, base 1, and base 2" refer to a Unijunction Transistor (UJT).