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: Gynaecology & Obstetrics
Which of the following events cause closure of ductus arteriosus in new born 
Select and explain. 
A. Compression of thorax during delivery, B. Compression of pulmonary vessels during delivery, C. Fall in pulmonary arterial pressure, D. Fall in systemic arterial pressure
C: Fall in pulmonary arterial pressure
Answer: C: Fall in pulmonary arterial pressure 
Explanation: Aeration of newborn lung causes rapid replacement of bronchial and alveolar fluid by air, with this compression of pulmonary vasculature is lowered which results in fall in pulmonary arterial blood pressure.
Thus ductus arteriosus closes.