Hi Maeverick,

The grammar rules behind Who/Whom are not very common on the GMAT (there's a good chance that you won't even see this rule on Test Day), but here's why the wrong answers are wrong:

This SC starts off with "Executives", which is plural. The "intent" of the sentence is that one of these executives is blind and that this person is going to demonstrate some equipment. So, it's ONE of these executives - we need to reference the individual and the plural that this person came from.

If we're going to refer to the "Executives", the word "who" won't match ("who" is singular); we need "whom"

Only Answer D matches.

A doesn't address the Executives
B is redundant (you don't need "one" and "who"; the word "them" is clunky)
C same problem as B
D Correct
E the word "which" is an incorrect pronoun for this situation

GMAT assassins aren't born, they're made,
Rich