Answer is A. I get why II is wrong. But why would antibodies from another mother help the infant? Wouldn't these antibodies be seen as foreign in the infant? Also, is vaccination actually ineffective for newborns in comparison to children?
But wouldn't the infant need breast milk from his/her mother only? Wouldn't the antibodies from someone else be recognized by the infant's body as foreign? (The infant still has his/her own IgM antibodies that can attack "foreign" matter, no?)