Discussion of greenhouse effects have usually had as a focus the possibility of Earth growing warmer and to what extent it might, but climatologists have indicated all along that precipitation, storminess, and temperature extremes are likely to have the greatest impact on people.
(This question is from Official Guide. Therefore, because of copyrights, the complete question cannot be copied here. The question can be accessed at GMAT Club)
- Discussion (Subject of First IC – Independent Clause)
- of greenhouse effects (prepositional phrase modifying “discussion”)
- have usually had as a focus (Verb – “have had”)
- the possibility of Earth growing warmer (modifies “focus”)
- and to what extent it might, (In a list with the previous element. Modifies “focus”)
- but climatologists have indicated all along that (Second IC. Subject – “climatologists”; Verb – “have indicated”)
- precipitation, (“That clause” Subject – 1)
- storminess, (“That clause” Subject – 2)
- and temperature extremes (“That clause” Subject – 3)
- are likely to have the greatest impact on people. (“That clause” Verb – “are”)
The sentence says:
Discussion of greenhouse effect has focused on the possibility that Earth may grow warmer and on the extent to which it might. However, climatologists have indicated that other factors are likely to have the greatest impact on people.
The sentence has the following errors:
- The singular subject “discussion” doesn’t agree with the plural verb “have had”.
- The structures “the possibility of Earth growing warmer” and “to what extent it might” are not parallel.
(A) Incorrect. For the errors described above.
(B) Incorrect. The structure “discussion has had as its focus X and Y” is much less clear than the structure in option C. Also, “to what extent” in option C is clearer and more concise than “what the extent would be” in this option.
This option doesn’t have any significant error. It is wrong just because option C is better qualitatively. We have to choose the best among the given options.
(C) Correct. The verb “has focused” is much clearer in communicating the meaning than the structures used in the previous two options. Also, “whether Earth…” is parallel to “to what extent”. Both are in question form, and both join the sentence at the same place i.e. “focused on whether Earth would grow warmer” and “focused on to what extent”.
(D) Incorrect. This option has the same two errors as option A has.
(E) Incorrect. “the extent that” lacks the clarity as to “extent of what”. Also, the use of simple present “is” is incorrect since the event is hypothetical.