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: Medicine
Sickle cell trait patient do not have manifestations as that of Sickle cell disease, because - 
Select and explain. 
A. 50% HbS is required for occurrence of sickling, B. HbA prevents sickling, C. 50% sickles, D. HbA prevents polymerazitation of Hbs
A: 50% HbS is required for occurrence of sickling
Answer: A: 50% HbS is required for occurrence of sickling 
Explanation: None