Bunuel wrote:

Since 1990 there are three times as many cases of West Nile virus diagnosed, and there has been no progress in the search for a vaccine.

(A) Since 1990 there are three times as many cases of West Nile virus diagnosed

(B) The diagnosis of cases of West Nile virus was only one-third in 1990

(C) The diagnosis of cases of West Nile virus has increased three times from 1990 on

(D) Tripling since 1990, there are now three times as many cases of West Nile virus diagnosed

(E) The number of diagnoses of West Nile virus has tripled since 1990

MANHATTAN REVIEW OFFICIAL EXPLANATION:

Choice A uses ‘since’ and the present tense. The present perfect is necessary. For example, ‘since 1990 there have been many cases...’. The correct subject of the sentence is ‘the number of diagnoses’, not ‘the diagnosis of cases’. Eliminate B and C. ‘Tripling’ in D is incorrect. Again the present perfect would have to be used to describe an action which started in the past and has continued up to the present. Choice E, the correct answer, shows this use of the present perfect. ‘The number...has tripled.’

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