So the argument is saying that it was not the science that led some trial to the wrong conclusion but rather a biased provision of data or some conflict of loyalties on the part of the forensic scientist in a particular case.
However, one could argue with this by saying that the conclusion that forensic science did not cause this miscarriage of justice is wrong because forensic science advocates some sort of prejudicial or biased provisioning of information or some sort of special allegiance to the prosecution. In effect, this should make clear that the author is assuming the bias is not somehow introduced by forensic science itself.
So (A) strengthens the argument by turning this assumption into a premise and thus ruling out a potential counterargument.
I hope this helps! I'd love if you could write out your explanations for why (B)-(E) are not good candidate answers, and this would be helpful for your own preparation too