A literacy mission holds that its evening centres are what raised adult reading in the block, since the villages with the most centres are the villages in which the share of adults able to read rose most. Which of the following, if true, most strengthens the mission's position?

A village-level pairing leaves open the awkward possibility that the villages with many centres improved for some reason of their own while the people who actually attended learnt nothing. Records kept name by name close that gap, and setting attenders against non-attenders of the same village removes whatever it is about a village that might otherwise explain the rise. Where the centres meet and how long the mission has worked describe the scheme; villages of a similar size make the figures tidier without saying anything about the adults within them.