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: Anaesthesia
Regarding variable orifice flowmeters true is 
Select and explain. 
A. The tube must be slightly inclined to the vertical to avoid friction, B. The bobbin is scored to avoid friction, C. Are accurate only for laminar flow, D. An orifice has diameter shorter than its length
B: The bobbin is scored to avoid friction
Answer: B: The bobbin is scored to avoid friction 
Explanation: The variable orifice flowmeter is rotameter. The tube is vertically mounted. the bobbin is scored so that it rotates without sticking. Tube is gas specific and laminar flow occurs at the base and turbulent flow occurs at the top.