## Core Concept
The question pertains to a specific sterilization technique using steam, which is a critical process in medical and laboratory settings to eliminate microbial life. The method described involves steam at 100 degrees centigrade for a specified duration and frequency.

## Why the Correct Answer is Right
The process described, involving steam at 100 degrees centigrade for 20 minutes on 3 consecutive days, is known as **tyndallization** or **fractional sterilization**. This method is used for sterilizing heat-sensitive materials that cannot withstand high temperatures. It works by using steam to kill vegetative cells, followed by a period that allows spores to germinate into more heat-sensitive vegetative cells, which are then killed in subsequent steam treatments.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is not specified, but if it's not tyndallization, it could be another method like autoclaving, which uses higher pressures and temperatures.
- **Option B:** Similarly, without specifics, if it's not the correct term for tyndallization, it doesn't apply.
- **Option C:** This could potentially be another sterilization method, but without details, it's hard to assess its accuracy.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **tyndallization** is specifically used for materials that are heat-sensitive and cannot be sterilized by high-pressure steam (autoclaving). This method is particularly useful in laboratories and medical facilities for sterilizing media and equipment that would be damaged by high temperatures and pressures.

## Correct Answer: D. Tyndallization.