If a man with type A blood marries a woman with type B blood. Their child is blood type O, then the genotypes of the parents are

The correct option is A AO and BO

In this case, as the blood group of Child is O, therefore it will be represented by (i${}^o$ i${}^o$) so each parent must have allele for O blood and it can be only possible in the case of crossing of (i${}^A$ i${}^o$) x (i${}^B$ i${}^o$). Hence option A is correct.