Smallpox and rabies are caused by:

Options

A. Virus
B. Protozoan
C. Typhoid
D. Polio

Answer

**Step-by-Step Solution:**

1. **Identify the Diseases**: The question asks about smallpox and rabies. We need to determine what causes these diseases.

2. **Research Smallpox**: Smallpox is known to be caused by a specific virus. The virus responsible for smallpox is called the variola virus.

3. **Research Rabies**: Rabies is another disease that is caused by a virus. The specific virus responsible for rabies is known as the rabies virus.

4. **Classify the Pathogens**: Both smallpox and rabies are classified as viral infections. This means they are caused by viruses, not by bacteria or protozoa.

5. **Analyze the Options**: The options provided are virus, protozoan, typhoid, and polio. Since we have established that both smallpox and rabies are caused by viruses, the correct answer must be "virus."

6. **Conclusion**: Therefore, smallpox and rabies are caused by viruses.

**Final Answer**: Smallpox and rabies are caused by viruses.

---