I think the answer you are looking for is <span> Salt and water.</span>
Blood types:
AB +
AB -
A +
A -
B +
B -
O +
O -
It is possible to have a child with O blood despite the parents having different blood types.
While the man tested for B blood, he could have been a combination between type o and B whereas, the woman was a combination of type A and o. Since A/B are dominant, they would 'stand out' contrarily to o.
This means that their children could have AB or O blood.
I do believe they made a mistake ???
