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: Radiology
Earliest radiological sign of pulmonary venous hypertension in chest X-ray is – 
Select and explain. 
A. Cephalization of pulmonary vascularity, B. Pleural effusion, C. Kerley B lines, D. Alveolar pulmonary edema
A: Cephalization of pulmonary vascularity
Answer: A: Cephalization of pulmonary vascularity 
Explanation: Cephalization of pulmonary vascularity is the first radiological sign of pulmonary venous hypertension amongst the options provided. Pulmonary venous hypertension results in diversion of blood flow from lung bases to the zipper lobes. This reversal of normal gravity dependent pattern and upper lobe venous diversion is first radiological sign.