What is eustachian tube? Give its function.

Explanation

### Step-by-Step Solution:

1. **Definition of Eustachian Tube**:
- The Eustachian tube is a narrow tube that connects the middle ear (specifically the tympanic cavity) to the pharynx (the back of the throat).

2. **Anatomical Location**:
- The Eustachian tube runs from the tympanic cavity of the middle ear to the nasopharynx, which is the upper part of the pharynx located behind the nose.

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