A city corporation reports that the free swimming lessons at its two pools were attended 12,000 times in June and 9,000 times in July, and its report concludes that at least 21,000 of the city's children were taught to swim over the two months. Which of the following, if true, most weakens the report's conclusion?

The corporation has counted sittings and concluded about children, and the option gives the exchange rate: twelve sittings to a child. On that footing the 21,000 attendances stand for something under two thousand children, and the report is out by a factor of ten. The city's stock of children of the right age would matter to a claim about coverage and does not touch the double counting; if anything it makes 21,000 sound possible and so lulls the reader. The number of times of day at which lessons were given describes the timetable of the pools and could not tell one attendance from another. And May being the heaviest month at the pools concerns a period outside the report altogether.