Appropriate techniques have been developed for large scale cell culture using bioreactors for producing :

Options

A. foreign gene product
B. vaccines
C. hormones
D. all of these

Answer

### Step-by-Step Solution:

1. **Understanding Bioreactors**: Bioreactors are specialized vessels designed to provide an optimal environment for the growth of cells or microorganisms. They are essential for large-scale cell culture as they allow for the controlled conditions necessary for cell growth and product formation.

2. **Purpose of Large-Scale Cell Culture**: The primary goal of using bioreactors for large-scale cell culture is to produce significant quantities of biological products. Small-scale cultures often do not yield enough product for commercial use, hence the need for bioreactors.

3. **Types of Products Produced**: Bioreactors can be used to produce a variety of biological products, including:
- **Foreign Gene Products**: These are proteins or enzymes produced from genetically modified organisms.
- **Vaccines**: Bioreactors can facilitate the mass production of vaccines by culturing the necessary cells or microorganisms.
- **Hormones**: Many hormones can be produced using biotechnological methods in bioreactors.

4. **Conclusion**: Given that bioreactors can be employed to produce foreign gene products, vaccines, and hormones, the correct answer to the question is that bioreactors are used for producing all of these products.

### Final Answer:
**All of these** (foreign gene products, vaccines, hormones).

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