Among the strategies our bodies have developed to keep our airways clean, it could be mentioned the hairs of our nouse, which avoid bigger particles to reach our lungs, but also a substance needed for this process is the pleural fluid, which covers the internal tissues of our lungs, and its epithelium to get those more little particles to not reach our alveoli, neutralizing them before.
The correct answer then is the first one: A. Pleural fluid in the thoracic cavity.
