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 disease true is -a) Mutation in α chainb) Symptoms ameliorated by HbFc) Venoocclusive crises is cause of morbidityd) Bone pain is presenting feature 
Select and explain. 
A. abc, B. bcd, C. ac, D. bd
B: bcd
Answer: B: bcd 
Explanation: None