Which choice most logically completes the text?

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Eastern Ohio's Monroe County is among the most rural counties in the United States: the US Census Bureau classified it as 97.7% rural in 2010. Researchers studying populations of counties like Monroe often struggle to recruit and retain participants. Melissa Valerio and colleagues tested whether a method called snowball sampling could improve recruitment and retention. Working in two rural counties, the researchers identified a small number of people who had the characteristics desired for a proposed study and asked them to recruit additional participants from their social networks.Valerio and colleagues found that participants recruited via snowball sampling showed a much higher retention rate than did people recruited by strangers, suggesting that ____

snowball sampling is more likely to improve retention rates among rural participants than among nonrural participants.

being recruited to participate in a study by someone with whom one is socially connected may impart a feeling of obligation to persist with participation in the study.

social networks can become large enough that two people can share a network but nevertheless regard each other as strangers.

people with relatively small social networks are inherently less likely to be recruited to participate in a study via snowball sampling than are people with relatively large social networks.