Common influenza is caused by

Options

A. virus
B. bacteria
C. Fungi
D. Protista

Answer

### Step-by-Step Solution:

1. **Identify the Disease**: The question asks about common influenza, which is commonly referred to as the flu.

2. **Understand the Options**: The options provided are virus, bacteria, fungi, and protista. We need to determine which of these is responsible for causing common influenza.

3. **Research the Causative Agent**: Common influenza is known to be caused by a specific type of virus. The most recognized virus responsible for influenza is the influenza virus.

4. **Recognize the Symptoms and Transmission**: The influenza virus primarily affects the respiratory system, including the nose, throat, and lungs. It spreads through respiratory droplets when an infected person sneezes or coughs.

5. **Conclude the Answer**: Based on the information gathered, the causative agent of common influenza is indeed a virus.

6. **Select the Correct Option**: Among the options given, the correct answer is option A: virus.

### Final Answer:
Common influenza is caused by a virus.

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