Circle the odd one out.
Pinna, Stirrup, Tympanum

Explanation

To solve the question "Circle the odd one out: Pinna, Stirrup, Tympanum," we will analyze each option step by step.

### Step 1: Identify what each term refers to.
- **Pinna**: The pinna is the external part of the ear. It is the visible part that collects sound waves and directs them into the ear canal.
- **Tympanum**: The tympanum, also known as the eardrum, is a membrane that separates the outer ear from the middle ear. It vibrates when sound waves hit it, allowing us to hear.
- **Stirrup**: The stirrup is a small bone in the middle ear (also known as the stapes). It is involved in the process of hearing but is not part of the outer ear.

### Step 2: Compare the functions and locations of each term.
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