**Core Concept**
Cystic fibrosis is a genetic disorder characterized by abnormal chloride ion transport across epithelial cells, resulting in thick, viscous secretions that obstruct various exocrine glands. This condition primarily affects the respiratory, gastrointestinal, and reproductive systems.

**Why the Correct Answer is Right**
The sweat glands in cystic fibrosis are not obstructed because they produce a different type of secretion compared to other exocrine glands. The sweat glands primarily secrete water and electrolytes, whereas the respiratory and gastrointestinal tracts produce thick mucus and viscous secretions, respectively. The abnormal chloride ion transport in cystic fibrosis leads to increased sodium absorption and water imbibition in sweat glands, resulting in normal or even increased sweat chloride levels, which is a diagnostic hallmark of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** The pancreas is obstructed in cystic fibrosis due to the abnormal thickening of pancreatic secretions, leading to pancreatic insufficiency and malabsorption of essential nutrients.

**Option B:** The lungs are obstructed in cystic fibrosis due to the accumulation of thick, viscous mucus in the airways, leading to recurrent respiratory infections and bronchiectasis.

**Option D:** The statement "All of above" is incorrect because it implies that all exocrine glandular ducts are obstructed in cystic fibrosis, which is not true for sweat glands.

**Clinical Pearl / High-Yield Fact**
Cystic fibrosis is caused by mutations in the CFTR gene, which encodes a chloride channel. The abnormal chloride ion transport in cystic fibrosis is a classic example of a "channelopathy," where a genetic mutation disrupts the normal function of a ion channel.

**✓ Correct Answer: C. Sweat gland**