Answer :
C. if the father was B, the mother was A, and the child had O, then the father had to be Bi and the mother had to be Ai
C. you can have an A or B blood type but also have recessive genes that could give an O if parent were heterozygous, like if the mother was A-i (i being recessive gene that could give 'O') and the father was B-i then if you do a punnett square then you can see that there's a 25% chance she has i-i or type O blood.