Which of the following is an INCORRECT statement regarding the structure of the human respiratory system?
- AThe trachea is a straight tube extending up to the mid-thoracic cavity, dividing at the level of the 5th thoracic vertebra.
- BThe primary bronchi are supported by complete cartilaginous rings.
- CThe pleural fluid reduces friction on the lung surface.
- DThe alveolar walls are extremely thin and richly supplied with blood capillaries.
✓ Correct answer: B
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