Harry suffers from cystic fibrosis and frequently has periods where he can hardly breathe. the problem is the result of
a) inflammation of the bronchi. constriction of the trachea.
b) thick secretions that exceed the ability of the mucus elevator to transport them.
c) laryngospasms that occur in response to a toxic substance produced by the epithelial cells.
d) collapse of one or both lungs.

b) Thick secretions that exceed the ability of the mucus elevator to transport them.

Explanation: In cystic fibrosis the primary defect  in ion transport leads to defective mucociliary action, and accumulation of thick viscid secretions  that obstruct the airways. This leads to a marked susceptibility to bacterial infections, which  further damage the airways. With repeated infections there is widespread damage to airway  walls, with destruction of supporting smooth muscle and elastic tissue, fibrosis, and further  dilatation of bronchi. The smaller bronchioles become progressively obliterated as a result of  fibrosis (bronchiolitis obliterans).

thick secretions that exceed the ability of the mucus elevator to transport it.

Explanation:

Let's have a brief explanation of the options.

Bronchitis inflammation is the inflammation of bronchial tubes which is caused by a viral or bacterial infection. Other factors may include smoking, air pollution e.t.c.

Tracheal Stenosis is the narrowing and constriction of the trachea. It can be caused by bacterial and fungal infections, external injury to the throat, autoimmune disorders (e.g polychondritis) e.t.c. Symptoms include coughing, difficult or labored breathing. But let's not forget that cystic fibrosis is a genetic disorder and not an autoimmune disorder. Therefore, constriction of the trachea is not the right answer.

thick secretions that exceed the ability of the mucus elevator to transport them is as a result of effect of Cystic Fibrosis. Cystic fibrosis (CF) is a genetic disorder that affects mostly the lungs, but also the pancreas, liver, kidneys, and intestine. Cystic fibrosis (CF) resulting from lungs disease causes clogging of the airways due to mucus build-up, decreased action of cilia in transporting mucus , and resulting  to inflammation.  (which cause injury and structural changes to the lungs, leading to a variety of symptoms).

There you have it!.