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: Medicine
The most common cause of acute cor pulmonale is: 
Select and explain. 
A. Pneumonia., B. Pulmonary thromboembolism., C. Chronic obstructive pulmonary disease, D. Primary spontaneous pneumothorax
B: Pulmonary thromboembolism.
Answer: B: Pulmonary thromboembolism. 
Explanation: Answer is B (Pulmonary thromboembolism): Most common causes of acute cor pulmonale is Pulmonary thromboembolism Most common cause of chronic cor pulmonale is Severe COPD