Following several years of declining advertising sales, the Greenville Times reorganized its advertising sales force. Before reorganization, the sales force was organized geographically, with some sales representativs concentrating on city-center businesses and others concentrating on different outlying regions. The reorganization attempted to increase the sales represntatives' knowledge of clients' businesses by having each sales representative deal with only one type of industry or of retailing. After the reorganization, revenue from advertising sales increased.

In assessing whether the imporvement in advertising sales can properly be attributed to the reorganization, it would be most helpful to find out which of the following?

标准答案是：(B) Has the circulation of the Greenville Times increased substantially in the last two years?

我不明白为什么过去两年报纸的发行量的增长可以用来衡量广告收入的增加是否应该归功于重组。