The following questions present a sentence, part of which or all of which is underlined. Beneath the sentence, you will find five ways of phrasing the underlined part. The first of these repeats the original; the other four are different. If you think the original is best, choose the first answer; otherwise choose one of the others.
These questions test correctness and effectiveness of expression. In choosing your answer, follow the requirements of standard written English; that is, pay attention to grammar, choice of words, and sentence construction. Choose the answer that produces the most effective sentence; this answer should be clear and exact, without awkwardness, ambiguity, redundancy, or grammatical error.
Because the key witness died just prior to the start of the trial, Detectives Mack and Smith were not able in determining the extent of administrative corruption.（）
A. Detectives Mack and Smith were not able in determining the extent of
B. therefore the detectives, Mack and Smith, were unable to determine the extent of
C. Mack and Smith, the detectives, were not able of determining the extent to
D. Detectives Mack and Smith were not able to determine the extent of
E. the extent was unable to be determined by Detectives Mack and Smith of
