Read the
Original Sentence Carefully, Looking for Errors:
This underlined portion contains a long descriptive phrase that separates the subject of the sentence, "the number," from its verb, "have greatly increased." The GMAT repeatedly uses long intervening phrases to mask any errors with subject-verb agreement. "The number" requires a singular verb, so "have" is incorrect.
Scan and Group the Answer Choices:
Using the verb at the end of each choice, group the choices into a 3-2 split. (A) and (B) end with “have” while (C), (D), and (E) end with “has.”
Eliminate Wrong Answer Choices:Eliminate (A) and (B). The subject of the clause for the verb “have” is “the number.” The word “number” can be used two ways: “a number of things” is plural while “the number of things” is singular. Since this sentence uses “the number of patients” in the non-underlined portion, the plural verb “have” is incorrect.
Examine the three remaining choices for another split. (C) uses "that"; (D) and (E) use "as." The construction "such..." in the non-underlined portion of the sentence must be followed by "...as...." Furthermore, the use of "that" makes the sentence say that illnesses use alternative treatments, which doesn't make sense. Eliminate (C).
(D) introduces an ambiguous modifier, another common error on the GMAT, with the phrase “using alternative, often homeopathic treatments.” As written, the phrase seems to modify "suffering." However, the intention of the sentence is that the patients are using the treatments to, presumably, alleviate suffering. Eliminate (D).
(E) uses the singular verb “has” and clarifies that the patients are using the treatments. It fits perfectly into the original sentence and is the
correct answer.
TAKEAWAY: The construction "... such ... as ..." is a frequently tested idiom on the GMAT. Also, mentally strip a long sentence down to its essential components—subject and predicate—to quickly identify errors obscured by intervening words.