Common cold is a

Options

A. bacterial disease
B. viral disease
C. protozoan disease
D. algal disease.

Explanation

To answer the question "Common cold is a:", follow these steps:

### Step 1: Understand the Options
The question provides four options: bacterial disease, viral disease, protozoan disease, and algal disease.

### Step 2: Identify the Nature of Common Cold
Common cold is primarily caused by viruses. The most common viruses that cause the cold include rhinoviruses and coronaviruses.

### Step 3: Eliminate Incorrect Options
- **Bacterial Disease**: Diseases like typhoid and cholera are caused by bacteria, not viruses.
- **Protozoan Disease**: Diseases such as malaria and sleeping sickness are caused by protozoa, which are single-celled organisms. Common cold does not fall under this category.
- **Algal Disease**: Algal diseases are caused by toxins from algae, which is not related to the common cold.

### Step 4: Confirm the Correct Answer
Since common cold is caused by viruses, the correct answer is "viral disease."

### Final Answer
Common cold is a **viral disease**.

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