A city's statistics bureau conducted a survey and analysis of the male-female ratio of the population within the city. The statistical results surprised them: the male-to-female ratio of the city 10 years ago was 1.02: 1, and now the ratio is rapidly rising to 1.39: 1 It is far higher than the national average of the city. Therefore, they believe that the work of the family planning department in this city has definitely had some problems in the past 10 years. If true, the one thing that would most weaken the conclusion of the Municipal Statistics Bureau is:. ["In fact, the city's family planning department attaches great importance to the issue of controlling the gender ratio of men and women. A meeting is held every year to study this issue.", 'Building materials (stone mining) and construction are the economic pillars of this city. In the past 10 years, these two industries have absorbed a large number of male migrant workers from other regions, and very few female migrant workers.', 'In the last 10 years, the private purchase of B-ultrasound in rural areas of the city to identify the sex of the fetus, leaving no baby girl, and only giving birth to a boy is very illegal.', "Ten years ago, the city's family planning department formulated a policy that stipulates that couples of childbearing age who only have one girl can receive corresponding financial rewards."]