Answer:
They could have all four type phenotype that are A, B, AB, and O
Explanation:
If the man has A blood group and the woman has B blood group then the genotype of man can be IAIA or IAi and the genotype of woman can be IBIB or IBi.
IA i
IB IAIB IBi
i IAi ii
So if the genotype of the parents are IAi and IBi then out of four offspring one could have AB blood group, second could have B blood group, third could have A blood group and fourth could have O blood group as shown in the cross above.