Well I’m fairly certain it’s D or blood type O.
Reasoning: If of parents have blood type O than there is really no way that the child can get blood type O. It can be A from one of the parents, B from one of the parents, or which is most common in this circumstance, an AB blood type. I’d compare it like to building legos. Can you build a millennium falcon if you don’t have the right legos? No, but you can combine the other two lego sets to make something else. Weird comparison but thats a very simple explanation of why
