BMAT 2016 Q 24 blood types + logical reasoning

Hi everyone,
The answer is D).

This is a worked solution if found:
There are only 4 different blood groups: A, B, AB and O.
The possibility of the criminal having blood group AB is: 25% (one out of the four possible blood groups).

However i disagree, the question seems to be asking P(AB knowing one allele is B) not P(AB) in general?
How would you interpret the phrasing of the question?

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