The presence of ............in the body induces the formation of antibodies.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks what induces the formation of antibodies in the body. Antibodies are crucial components of the immune system that help protect the body from foreign substances.

2. **Identifying Antibodies**: Antibodies are proteins produced by the immune system in response to foreign substances. They play a key role in identifying and neutralizing pathogens such as bacteria and viruses.

3. **Role of Antigens**: The foreign substances that trigger the immune response are known as antigens. Antigens can be toxins, chemicals, or parts of pathogens like bacteria and viruses.

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