This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardio thoracic surgery  , Subject name: Surgery
[{'content': 'Heimlich valve is used for drainage of \nSelect and explain. \nA. Pneumothorax, B. Hemothorax, C. Emphyema, D. Malignant plural effusion', 'role': 'user'}, {'content': "Answer: A \nExplanation: The Heimlich valve(flutter valve)is a small one-way valve used for chest drainage that empties into a flexible collection device & prevents return of gases or fluids into the pleural space.The heimlich valve is less than 13 cm long and facilitates patient ambulation. Reference:SRB's manual of surgery,5th edition,page no:1116.", 'role': 'assistant'}]