I would say it's A because it sounds like the most important one.
Replication occurs in three major steps: the opening of the double helix and separation of the DNA strands, the priming of the template strand, and the assembly of the new DNA segment. During separation, the two strands of the DNA double helix uncoil at a specific location called the origin.
Answer:
25% type A, 25% type B, 25% type AB, 25% type O
If you put it into a punnett square:
B O
A AB AO
O BO OO
you get 25% for each phenotype
The answer to this particular question is A