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
In colour doppler the color depends upon: 
Select and explain. 
A. Strength of returning echo, B. Relation of transducer to blood flow, C. Frequency of doppler used, D. Type of doppler machine used
B: Relation of transducer to blood flow
Answer: B: Relation of transducer to blood flow 
Explanation: Ans. Relation of transducer to blood flow