This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Following is true about cystic Fibrosis 
Select and explain. 
A. Nasal polyposis is absent, B. Sweat chloride levels > 30 mmol / L is diagnostic, C. Staphylococcus is most common pathogen  causing  infection in cystic fibrosis in adults., D. Chromosome - 7 genetic defect
D: Chromosome - 7 genetic defect
Answer: D: Chromosome - 7 genetic defect 
Explanation: In adults pseudomonas is most common arganism causing infection in cystic fibrosis adult patients.
Sweat chloride levels > 60 mmol / L is diagnostic.
Nasal polyps is present.