pyq/2011/prelims/66

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 -

(A) O positive

(B) A positive

(C) B positive

(D) Cannot be determined on the basis of the given data