GMAT Sentence Correction (SC) | Re: Handwriting analysis has recently been boosted by the

I do agree that this is not an error- free question.
There are grave doubts about choice A and for that matter even about B.
1. Addition of a verb ‘are’ isn’t going to be helpful since it is not the strokes that are not detectable but indeed the starting and ending points that are not detectable. But a modifier, not preceded by a comma has to modify its proximate noun, strokes in this case.
A verb is not going to serve any purpose in an infinitive phrase as we have in this example.
B
...

---