Contamination, vaccination, immunization, healthy diet.

Explanation

### Step-by-Step Solution:

1. **Identify the Terms**: The four terms given are contamination, vaccination, immunization, and healthy diet.

2. **Define Each Term**:
- **Contamination**: This refers to the process of making something impure or unclean, often through pollution. For example, industrial waste can contaminate water sources.
- **Vaccination**: This is a medical treatment where a vaccine is introduced into the body to provide immunity against a specific disease. It involves administering a weakened or dead form of a microbe.
- **Immunization**: This is the process of making a person or animal immune to an infectious disease, often through vaccination. It helps the body recognize and fight off the disease-causing agents.
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