Bunuel
It is more effective for the union as a group to address a grievance to management than for multiple individual employees to do so.
(A) It is more effective for the union as a group to address a grievance to management than for multiple individual employees to do so
(B) It is more effective when the union as a group addresses a grievance to management than multiple individual employees doing it
(C) The union as a group addressing a grievance to management has a greater effect than the multiple individual employees who address it
(D) By addressing a grievance to management, the union as a group is more effective than when multiple individual employees do it
(E) A grievance to management is most effectively addressed by the union as a whole, instead of by multiple individual employees
Official Explanation:Choice (A): this choice correctly compares two infinitive phrases, beginning with the subject of the infinitive in a "for" preposition. This choice correctly uses the "empty it" construction, because the main predicate "is effective" is very short compared to the two infinitive phrases. This choice also uses the correct abbreviated phrase for repeating a predicate. This is correct on all fronts.
Choice (B): this choice violates parallelism by comparing a "when" clause to a gerund phrase. Also, this uses the incorrect abbreviation "doing it" in its attempt to repeat a predicate. This is incorrect.
Choice (C): The phrase "has a greater effect" is grammatically correct but a little awkward. The nature of the comparison is unclear here: it seems to compare the action of the union to the people, the "multiple individual employees." We know what this one is trying to say, but it doesn't say it in the most effective way. This is incorrect.
Choice (D): this choice violates parallelism by comparing "the union" to a "when" clause. Also, this uses the incorrect abbreviation "doing it" in its attempt to repeat a predicate. This is incorrect.
Choice (E): The passive structure is unusual in this. We absolutely cannot have the object of "instead of" be another prepositional phrase—"instead of by multiple individual employees." The GMAT seems to avoid completely comparisons with "instead of", using "rather than" in almost all of those situations. This is incorrect.
The only possible answer is (A).