Interrogative which (whether adjectival or pronominal) may be used with reference to either the Subject or an Object (Direct or Indirect) of its corresponding indicative sentence.
If used of an Object, which is followed by an inversion of the indicative sentence, with DO-support if the head verb is not an auxiliary:
This context may reflect that definition. ... Which definition may this context reflect?
This context demands that definition. ... Which definition does this context demand?
If used of the Subject, which simply replaces either the Subject or its determiner:
This context demands that definition. ... Which (context) demands that definition?
This is your grammatically correct A form.
Note that it is the syntactical role of the referent as Subject or Object, not its semantic role as Agent or Patient (or Recipient) which governs which form is used. If you passivize the sentence and make the referent object its subject, it takes the second, non-inverted form:
This context demands that definition. > This definition is demanded by that context. > Which (definition) is demanded by that context?
Note also that the switch from "most accurate" in A to "more accurate" in B needs to be tidied up. If only two choices are presented, use "more". If more than two choices, use "most". – toandfro – 2013-11-18T20:19:21.377
1+1: I think your answer best addresses the issue of why OP's B isn't acceptable, and shows the least possible change to make it so. In a case like this, I think it's worth showing how OP's existing knowledge/understanding of English grammar can be leveraged to achieve a "valid" form, rather than proposing more radical reworkings that might actually sound more natural to native speakers. – FumbleFingers Reinstate Monica – 2013-03-03T02:15:06.617