Which o the following statements is not true about the respiratory mucosa?
a. the cilia can "taste" bitter toxins in the air.
b. the cilia respond to toxins by moving more rapidly to remove the toxin.
c. the longer a cilia is exposed to a toxin, the more effectively it moves to expel it.
d. all of the above statements are true about the respiratory mucosa.

The correct answer is option C.

Explanation:

Cilia are tiny hair-like projections or appendages on the surface of the outside of the cells, in respiratory tract cells not move on which cilia are present, however, these projections are helpful in moving debris like microorganisms like bacteria, dust, and toxins out of the lungs.

Cilia can sense bitter toxins or substances in the air and remove or expel it, these present on the epithelial cells in the human airway that taste bitter compounds remove it. Cilia moving more rapid in turn of toxin response. The exposure time has no effective role in expelling the toxin by cilia.

Thus, the correct answer is option C.