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
[{'content': 'Secondary retrosternal goitre derives its blood supply from : \nSelect and explain. \nA. Mediastinal vessels, B. Thyroid vessels, C. Arch of aorta, D. Bronchial vessels', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Secondary retrrosternal goitre : Is the extension of thyroid tissue to mediastinum from thyroid in the neck. and it derives blood supply from thyroid vessels.\nPrimary\xa0retrrosternal goitre : Is the ectopic thyroid tissue in the mediastinum and it derives blood supply from mediastinal vessels.', 'role': 'assistant'}]