A Married Couple Adopted a Male Child, A few years later; Twin Boys Were Born to them

A married couple adopted a male child, A few years later; twin boys were born to them. The blood group of the couple is AB positive and O negative. The blood group of the three sons is A positive, B positive, and O positive. The blood group of the adopted son is(2011)

a) O positive

b) A positive

c) B positive

d) Cannot be determined on the basis of the given data

Answer: A

Parents with AB positive and O negative will not have child with blood group O positive.