Which of the following components can consist of three regions of semiconductor material?

Bipolar junction transistors (BJTs) are constructed using three distinct layers of doped semiconductor material. These are arranged either as NPN (Negative-Positive-Negative) or PNP (Positive-Negative-Positive), and these three regions correspond to the transistor's emitter, base, and collector terminals. Triodes and pentodes also have three and five functional elements respectively, but they are vacuum tubes, not solid-state semiconductor devices. An alternator is an electromechanical generator, completely unrelated to three-region semiconductors.