**Core Concept**
Chronic lymphoedema of the limb, also known as elephantiasis, is a condition characterized by the chronic swelling of a limb due to the obstruction of lymphatic vessels. This leads to chronic inflammation, fibrosis, and thickening of the skin, making it prone to various complications.

**Why the Correct Answer is Right**
Marjolin's ulcer is a type of squamous cell carcinoma that typically arises from a burn scar or chronic wound, not from chronic lymphoedema. The development of Marjolin's ulcer is associated with prolonged exposure to chronic inflammation and scarring, which is not a characteristic feature of chronic lymphoedema. In contrast, chronic lymphoedema is more commonly associated with recurrent soft tissue infections, thickening of the skin, and an increased risk of sarcoma, particularly lymphangiosarcoma.

**Why Each Wrong Option is Incorrect**
**Option A:** Thickening of the skin is a common feature of chronic lymphoedema due to chronic inflammation and fibrosis, making it a correct association.
**Option B:** Recurrent soft tissue infections are a well-known complication of chronic lymphoedema, as the lymphatic obstruction leads to the accumulation of protein-rich fluid, creating an ideal environment for bacterial growth.
**Option D:** Sarcoma, specifically lymphangiosarcoma, is a rare but recognized complication of chronic lymphoedema.

**Clinical Pearl / High-Yield Fact**
Chronic lymphoedema is often associated with a higher risk of developing lymphangiosarcoma, also known as Stewart-Treves syndrome, particularly in the absence of a clear primary malignancy. This emphasizes the importance of regular follow-up and surveillance in patients with chronic lymphoedema.

**✓ Correct Answer: C. Marjolin' s ulcer**