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: Unknown
The least amount of fetal Rh+ve blood needed to cause isoimmunization in a Rh negative mother is - 
Select and explain. 
A. 0.1 ml, B. 0.01 ml, C. 0.001 ml, D. 10 ml
A: 0.1 ml
Answer: A: 0.1 ml 
Explanation: Ans: A