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
_______________ of Fluid is required to produce costophrenic angle bluting** on erect chest X-ray, in cases of pleural effusion: 
Select and explain. 
A. 100ml, B. 300ml, C. 500ml, D. 750ml
B: 300ml
Answer: B: 300ml 
Explanation: At least 100ml of fluid is required to detect by USG.
A minimum of 300ml is required to produce bluttening of costophrenic angle on erect chest X-ray.
About 500ml of effusion is required for detection on clinical examination.