Hey All,
There's been plenty of good discussion on this one, but just to put it all in one place, I'm stepping in. Also, lots of people mentioned concision on this one. There is not a single concision issue here. Concision is a SHOCKINGLY rare issue on the GMAT. Only fall back on it as a last resort.
300.Following the destruction of the space shuttle Challenger, investigators concluded that many key people employed by the National Aeronautics and Space Administration and its contractors work an excessive amount of overtime that has the potential of causing errors in judgment.
(A) overtime that has the potential of causing
PROBLEM: The relative pronoun "that" is opening up a modifier on "overtime" which is problematic from a meaning perspective. What the sentence wants is for the modifier to modify "an excessive amount of overtime", but right now it reads as modifying "overtime". In other words, the sentence sounds like the contracts are working an excessive amount of a SPECIFIC (essential) kind of overtime, the kind that has the potential of causing errors in judgment. This is incorrect. Also, "of" is the wrong idiom with potential.
(B) overtime that has the potential to cause
PROBLEM: Same as above, though it fixed the idiom issue.
(C) overtime that potentially can cause
PROBLEM: Same as above. The adverb "potentially" is okay, though the placement is incorrect. We need to place it after "can" if we don't get any commas. Consider these examples: "He is potentially the greatest boxer of all time" is better than "He potentially is the greatest boxer of all time."
(D) overtime, a practice that has the potential for causing
PROBLEM: Now we are using an appositive modifier (modifying a noun with a noun "a practice..."), which is clearer. The "practice" is the entire phrase "work(ing) an excessive amount of overtime". Unfortunately, the idiom is correct after "potential" (should be "to").
(E) overtime, a practice that can, potentially, cause
ANSWER: People don't like picking things with too many commas. BUT COMMAS ARE GREAT! Commas are not bad or wordy. They are how we separate ideas in English. The more commas, often, the better. "potentially" is modifying "can cause", and we often set off modifiers with commas on either side.
Hope that helps!
-t