Since Mary has a Type A blood, she is either AA or AO while John is either BB or BO. Since both John's parents are Type AB, he can only have the either A or B as an allele and not O so he is BB. Since John can only give the B allele, all of his children must have the B allele in their blood types. So the adopted one is the child with type A blood.
I took the test the answer (for sure) is c: programmed cell death. Good Luck!
