## Core Concept
Cryopreservation of semen involves cooling it to very low temperatures to preserve its viability for future use. This process is crucial in semen banks for storing and maintaining the fertility potential of individuals. The method used for preserving semen at low temperatures involves specific cryoprotectants.

## Why the Correct Answer is Right
The correct answer, **Liquid Nitrogen (-196°C)**, is used because it provides the lowest temperature required for the cryopreservation of semen. At this temperature, all metabolic processes come to a near standstill, effectively preserving the semen. Liquid nitrogen is commonly used in cryogenics for preserving biological samples, including sperm, eggs, and embryos, due to its ability to achieve and maintain extremely low temperatures.

## Why Each Wrong Option is Incorrect
- **Option A:** While glycerol is indeed a cryoprotectant used in the freezing of semen to prevent ice crystal formation and protect cell membranes, it is not the method used for preserving semen at low temperatures but rather an additive to the semen during the freezing process.
- **Option B:** Dimethyl sulphoxide (DMSO) is another cryoprotectant that can be used in cryopreservation, particularly for certain types of cells and tissues. However, it is not the method of preservation itself but a substance that may be added to protect cells during freezing.
- **Option D:** Although DMSO and glycerol are both used as cryoprotectants, and DMSO is mentioned here again, it's clear there's confusion with the role of substances in the preservation process versus the method of preservation.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the use of liquid nitrogen for cryopreservation allows for the long-term storage of biological samples without significant loss of viability. This technology is crucial for fertility preservation and assisted reproductive technologies.

## Correct Answer: C. Liquid Nitrogen (-196°C).