Explanation: Full quieting refers to the point where an FM receiver is receiving a signal strong enough that the receiver's background noise is completely suppressed, making the audio clear and quiet. This phenomenon is a key characteristic of FM reception. FM receivers utilize a limiter stage that clips amplitude variations, including most noise, before the signal goes to the discriminator. When the received signal is significantly stronger than the noise floor, the limiter effectively removes the noise, resulting in a very high signal-to-noise ratio (SNR) at the output. This causes a dramatic reduction in the perceived background hiss, making the receiver "quiet." * **A) Adjusting the squelch control to eliminate background noise.** Squelch is a gate that mutes the receiver when no signal is present or when the signal is too weak. Full quieting describes the *effect of a strong signal* making the noise disappear *during reception*, not a manual adjustment to mute an absent signal. * **B) The rapid decrease in SINAD and noise with increasing signal level.** This is incorrect. Full quieting is characterized by a *rapid increase* (improvement) in SINAD and a *decrease* in noise as the signal level rises. * **D) The rapid improvement in SINAD and decrease in noise with decreasing signal level.** This is also incorrect; the opposite is true. As signal level decreases, SINAD degrades, and noise increases.