If there is one thing that could halt the ascent of social networks, it is the thorny question of privacy. This is (62) because it goes right to the heart of the social-networking business model, In order to (63) users, sites need to offer ways for members to restrict the information about themselves that gets shared with a wider (64) . But if a site allows members to keep too much of their information private, there will be less traffic that can be turned into profit (65) advertising and various other means, (66) the network’s business will suffer.There is some evidence that people are starting to become more sophisticated about the Way in which they (67) their data, which could have longer-term (68) for the networks’ growth, Research (69) last year showed that some 60% of adults are restricting (70) to their online profiles.As it happens, the social networks have partly brought this on themselves. In order to offer a better service, many have created (71) sets of privacy controls that allow users to switch (72) different levels of protection to entrench (保护) their online data. Facebook has excessive controls that can be (73) to create different levels of confidentiality. Default settings (默认设置) for younger people on social-networking sites are often more 74 than those for adults to ensure they are protected 75 unwanted attention.Social networks (76) applause for developing these fine-grained controls. (77) their desire for profit can put them on a (78) course with privacy activists, regulators and their users. One bone of contention is social networks’ (79) to draw attention to their privacy statements. The reason for this might be (80) about "privacy reassurance": the worry that alerting people to privacy as a potential issue will make them less inclined to share things, (81) robust privacy controls are available. 64（）

A. society
B. public
C. coverage
D. audience