**Core Concept**
Gardner's syndrome is a rare, hereditary disorder characterized by multiple intestinal polyps, osteomas (bone tumors), and other soft tissue tumors. This condition is a variant of familial adenomatous polyposis (FAP), which is a well-known genetic disorder that predisposes individuals to colorectal cancer.

**Why the Correct Answer is Right**
Gardner's syndrome is caused by mutations in the APC gene, which is a tumor suppressor gene. The APC gene normally helps regulate cell growth and division, but mutations in this gene can lead to uncontrolled cell growth and tumor formation. The characteristic features of Gardner's syndrome include multiple polyps in the colon, osteomas (especially in the jaw and skull), epidermal inclusion cysts (a type of skin tumor), and fibrous tumors in the skin. These tumors are benign, but they can be disfiguring and may increase the risk of developing colorectal cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while polyposis of the colon is a feature of Gardner's syndrome, cancer of the thyroid is not a characteristic feature of this disorder. Thyroid cancer is more commonly associated with multiple endocrine neoplasia (MEN) syndromes.

**Option B:** This option is incorrect because polyposis of the jejunum is not a characteristic feature of Gardner's syndrome. The jejunum is a part of the small intestine, and Gardner's syndrome primarily affects the colon. Additionally, pituitary adenoma is not a typical feature of this disorder.

**Option D:** This option is incorrect because while polyposis of the gastrointestinal tract is a feature of Gardner's syndrome, cholangiocarcinoma (a type of bile duct cancer) is not a characteristic feature of this disorder. Cholangiocarcinoma is more commonly associated with primary sclerosing cholangitis or chronic bile duct inflammation.

**Clinical Pearl / High-Yield Fact**
Gardner's syndrome is a rare variant of FAP, and its diagnosis can be challenging. A high index of suspicion is necessary, especially in patients with a family history of FAP or colorectal cancer. Early diagnosis and treatment can help prevent colorectal cancer and other complications associated with this disorder.

**✓ Correct Answer: C. Polyposis colon, osteomas, epidermal inclusion cysts and fibrous tumours in the skin**