A certain library was experiencing a problem with lost books,

A certain library was experiencing a problem with lost books, which depleted the library of approximately 2 percent of its collection every year. In the spring, the director of the library instituted a new system of far heavier fines for library patrons who lost books. After three months of operation under the new system, the director announced that the new system, although unpopular, was working. As evidence, he stated that the number of books reported lost during the three-month period was only one-third the number that had been reported lost during the preceding three months.
Which of the following, if true, casts the most doubt on the director's claims about the effectiveness of the new system?
A. In the past, the number of books reported lost during any three-month period tended to fluctuate as much as 50 percent up or down.
B. Several of the library's patrons, angered by the severity of the new system, had petitioned the library's governing board to have the director fired.
C. Children under fifteen years of age, the age-group of patrons most likely to lose books, on average borrow twice as many books during the summer as they do during the rest of the year when they are in school.
D. Some patrons, in order to avoid the increased fine, delayed reporting their books lost in the hopes that they eventually might find the books.
E. Although the fine for a lost book was substantially greater during the three-month period than it had been previously, the library's revenue derived from lost-book fines decreased over the period.