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: Surgery
The brilliantly transilluminant tumour in the neck may be- 
Select and explain. 
A. Branchial cyst, B. Thyroglossal cyst, C. Sternomastoid tumour, D. Cystic hygroma
D: Cystic hygroma
Answer: D: Cystic hygroma 
Explanation: None