## **Core Concept**
The sonic system, often related to medical devices or diagnostic tools, utilizes specific frequencies for its operation. In medical contexts, the term "sonic" often relates to sound waves, which can be used in diagnostic imaging or therapeutic procedures. Understanding the frequency at which such systems operate is crucial for their effective application.

## **Why the Correct Answer is Right**
The correct answer, **C. 20 kHz and higher**, is right because sonic systems, particularly those used in medical diagnostics or therapeutics (like ultrasonic devices), operate at frequencies above 20 kHz. This range is considered ultrasonic or supersonic, beyond the upper limit of human hearing, which is approximately 20 kHz. Devices operating at these frequencies can be used for imaging (e.g., ultrasound) or for cleaning and therapeutic purposes.

## **Why Each Wrong Option is Incorrect**
- **Option A: 20 Hz to 20 kHz** - This range represents the audible spectrum for humans, which is below the frequency range for sonic systems used in medical diagnostics or therapeutics that require ultrasonic frequencies.
- **Option B: 1 Hz to 10 Hz** - This range is extremely low and corresponds to infrasound, which is not relevant to the operation of sonic systems in medical contexts.
- **Option D: 1 MHz to 10 MHz** - While this range is indeed ultrasonic and used in some medical imaging (like ultrasound), it is more specific and not the broad range that characterizes the operational spectrum of sonic systems.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that ultrasonic devices used in medicine, such as for cleaning, imaging, or lithotripsy, operate at frequencies above 20 kHz, typically in the range of **20 kHz to 10 MHz**. This high-frequency range allows for the generation of focused ultrasound waves that can be used for therapeutic or diagnostic purposes without causing harm.

## **Correct Answer: C. 20 kHz and higher**