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
True about aetiopathogenesis of Alzheimers disease-a) Absence of tau proteinb) Involvement of Apolipoprotein Ec) Preseneline-1and 2 involved  d) Mutation in chromosome 21e) Preseneline 2 is not involved 
Select and explain. 
A. abc, B. bcd, C. ac, D. bd
B: bcd
Answer: B: bcd 
Explanation: None