## Core Concept
Cystoscopes and bronchoscopes are medical instruments used for examining the interior of the bladder and lungs, respectively. These instruments are classified as **endoscopes** and are made of materials that can withstand various sterilization methods but require careful handling to prevent damage. The sterilization method for such delicate equipment must effectively kill bacteria, viruses, and other pathogens without damaging the instrument.

## Why the Correct Answer is Right
The correct answer involves **glutaraldehyde**, a high-level disinfectant widely used for sterilizing heat-sensitive equipment, including endoscopes like cystoscopes and bronchoscopes. Glutaraldehyde works by cross-linking proteins and disrupting cell membranes, effectively killing bacteria, viruses, and fungi. It is particularly useful for delicate medical instruments that cannot be sterilized using high-temperature methods like autoclaving.

## Why Each Wrong Option is Incorrect
- **Option A:** Autoclaving involves high pressure and temperature, which can damage heat-sensitive equipment like cystoscopes and bronchoscopes.
- **Option B:** Ethylene oxide gas sterilization is used for materials that are heat-sensitive but can be damaged by liquid chemicals; it's more commonly used for sterilizing disposable medical supplies.
- **Option D:** Ultraviolet (UV) light disinfection is not suitable for complex instruments like endoscopes as it may not reach all areas and is less effective against certain pathogens.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **glutaraldehyde** is a commonly used agent for high-level disinfection of endoscopes, but the process requires careful adherence to the manufacturer's instructions, including exposure time and rinsing procedures, to ensure effectiveness and safety.

## Correct Answer Line
**Correct Answer: C. Glutaraldehyde**.