What blood type should the parents of type o blood be?

The child's blood type depends on the antigen on the parent's blood type. If the child is o blood type, it means that there is only one pair of chromosomes. According to the rules of blood type inheritance, the child's parents cannot be Ab blood type. Both may be o blood type. Their blood type gene only has o gene. It is also possible that one of them is b blood type, the other is o blood type, or both are b blood type.