Cryopreservation is .
A. preservation at ultra low temperature
B. preservation in liquid nitrogen
C. preservation through exposure to gamma rays
D. preservation of semen

Options

A. A and B
B. B and C
C. C and D
D. A, B, C,D

Answer

To solve the question regarding cryopreservation, we will analyze each option provided:

1. **Understanding Cryopreservation**: Cryopreservation is a method used to preserve cells, tissues, or any biological constructs by cooling them to very low temperatures. This process helps in maintaining the viability of the cells for future use.

2. **Analyzing the Options**:
- **Option A: Preservation at ultra low temperature**: This statement is true. Cryopreservation involves preservation at ultra-low temperatures, typically around -196 degrees Celsius.
- **Option B: Preservation in liquid nitrogen**: This statement is also true. Liquid nitrogen is commonly used in cryopreservation as it can maintain the required ultra-low temperatures.
- **Option C: Preservation through exposure to gamma rays**: This statement is false. Gamma rays are used for sterilization and not for cryopreservation.
- **Option D: Preservation of semen**: This statement is true. Cryopreservation is often used to preserve semen for artificial insemination and other reproductive technologies.

3. **Conclusion**: Based on the analysis:
- Options A, B, and D are correct.
- Option C is incorrect.

Thus, the correct answer is **A, B, and D**.

### Step-by-Step Solution:
1. Define cryopreservation and its purpose.
2. Evaluate each option:
- Check if cryopreservation involves ultra-low temperatures (True).
- Check if it involves preservation in liquid nitrogen (True).
- Check if it involves exposure to gamma rays (False).
- Check if it involves preservation of semen (True).
3. Identify the correct options based on the evaluations.
4. Conclude that A, B, and D are correct.