What are three common oscillator circuits?

The Colpitts, Hartley, and Pierce circuits are the three most common LC and crystal oscillator topologies used in radio design. The Colpitts oscillator uses a capacitive voltage divider for feedback, the Hartley uses an inductive voltage divider (a tapped coil), and the Pierce uses a quartz crystal in its feedback path. The distractors use made-up or unrelated names to confuse test-takers. For example, "Fenner and Beane" combined with "Pierce" is actually a reference to a historic stock brokerage firm (Merrill Lynch, Pierce, Fenner & Beane), making it a classic joke by the exam committee. Learning these three names is foundational for RF design, as almost all traditional variable frequency and crystal oscillators in amateur radio gear are variations of these three core circuits.