Mucus plays an important role in cleansing inhaled air. it is produced by of the respiratory tract.
a. squamous alveolar cells
b. great alveolar cells
c. the pleurae
d. goblet cells

Goblet cells

Explanation: Respiration can be defined as the process by which gaseous exchange takes place between the atmosphere and body.

Respiratory system consists of two parts upper part and lower part. The upper part of the respiratory tract includes nasal passage from where the air gets in. This air contains dirt and harmful microorganism that is stopped there only by the help of mucus.

Mucus is secreted by the goblet cells, which is simple columnar epithelial cells that helps in producing gel forming mucins. Goblet cells are mainly found in the respiratory,gastrointestinal  and reproductive tract of the body.

So, the correct answer is Goblet cells.

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