If the cause of disease is living entity, it is called

Options

A. toxin
B. toxoid
C. virus
D. pathogen

Answer

To solve the question "If the cause of disease is a living entity, it is called," we need to analyze the provided options and understand the definitions of each term.

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for the term that describes a cause of disease that is a living entity.

2. **Review the Options**:
- **Option 1: Toxin** - A toxin is a poisonous substance that can cause harm but is not a living entity. Thus, this option does not fit the criteria.
- **Option 2: Toxoid** - A toxoid is an inactivated toxin used in vaccines. It is also not a living entity, so this option is incorrect.
- **Option 3: Virus** - A virus can be considered a living entity when it infects a host, but it is often classified differently in biological terms. However, it does not fit the broader definition of a living organism causing disease.
- **Option 4: Pathogen** - A pathogen is defined as any living agent, such as bacteria, viruses, fungi, or parasites, that can cause disease. This option directly matches the question's criteria.

3. **Choose the Correct Answer**: Based on the analysis, the correct answer is **Pathogen**. A pathogen is specifically a living entity that causes disease.

### Final Answer:
If the cause of disease is a living entity, it is called a **Pathogen**.

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