The PCD is an abbreviation used for the primary cilia diskinesia disease. This condition result in the reduced motility of the cilia.
In respiratory tract, the cilia help the mucus to flow above the respiratory tract. In case, the cilia is damaged, or it is not able to move, then the mucus cannot move out of the respiratory tract and cause many respiratory abnormalities, such as congestion, infection, bronchitis, cough, short of breath, ear infections etc.
The answer is d because it makes sense
This disorder can be caused by a reverse transcriptase enzyme not working properly or a transcriptase enzyme not working properly, because these enzymes are required to transfer RNA into DNA and vice versa.
Well there are three reasons
it drains into rivers, streams, etc. or
it seeps into soil and gather underground as ground-water
or
falls into high mountains and freeze and in the summer it will melt and flows into the rivers