## Core Concept
Sterilization of materials, especially those that are heat-sensitive like oils and greases, requires methods that do not involve high temperatures. **Sterilization** is a process that eliminates all forms of microbial life. For materials that cannot withstand autoclaving or dry heat sterilization, alternative methods are used.

## Why the Correct Answer is Right
The correct answer, **dry heat sterilization**, is suitable for materials that are heat-stable but cannot get wet, such as oils, greases, and powders. This method involves using hot air to kill microorganisms. The process typically uses a **hot air oven**, which can reach temperatures of 160°C to 200°C. This method is effective for sterilizing non-aqueous substances that can withstand high temperatures but not moisture.

## Why Each Wrong Option is Incorrect
- **Option A:** Autoclaving involves high-pressure steam and is not suitable for oils and greases because they do not mix with water and cannot be effectively sterilized by steam.
- **Option B:** Pasteurization is a process that reduces the number of pathogenic microorganisms and is typically used for liquids like milk and juice, not for oils and greases.
- **Option D:** Ethylene oxide gas sterilization is used for heat-sensitive and moisture-sensitive materials but is more commonly used for pre-packaged or wrapped items that are not easily penetrated by dry heat.

## Clinical Pearl / High-Yield Fact
A key point to remember is that when choosing a sterilization method, the material's properties and the potential impact on its integrity must be considered. Oils and greases are best sterilized using **dry heat** to avoid degradation and to ensure they remain effective for use.

## Correct Answer: C.