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Because the child's RBC has agglutinated with an Anti-B then he must have B antigen on the surface of RBC.
Because the child's RBC has not agglutinated with Anti-D antibodies then there's no D antigen on the RBC surface.
Similarly his serum must have anti-A antibodies as it agglutinated A RBC and should have no Anti-D antibodies as it did not agglutinate D RBCs.
Conclusion: the child is B -ve

Father AB- X Mother Bb- => these possibilities; AB-, Ab-, BB-, Bb-
So there's 50% chance that the baby will be B- and the best answer is choice A.

However, they should not say the "child IS the natural offspring" because blood grouping is only suggestive of paternity and is not conclusive and the options should say the child Maybe or probably or likely ...etc
 

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I think it is A too, but technically, B could also be true especially if it actually stated "The Mother is the biological mother but the father may or may not be the biological father," since the child could have inherited his B-ve blood group either from his AB-ve father as well as from a BO-ve mailman.

No judgements though... :)
hahaha, what do you mean by mailman? do you think that the mother has a relation with the guy that delivers the mail :confused:
 
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