What does the word they” in paragraph 3 refers to.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 35 to 42.
Social networking sites like Facebook and MySpace do not help you make more genuine close friends, according to a survey by researchers who studied how the websites are changing the nature of friendship networks. Although social networking on the internet helps people to collect hundreds or even thousands of acquaintances, the researchers believe that face to face contact is nearly always necessary to form truly close friendships.
"Although the numbers of friends people have on these sites can be massive, the actual number of close friends is approximately the same in the face to face real world," said Will Reader at Sheffield Hallam University. Social networking websites such as Facebook, Bebo and MySpace have taken off rapidly in recent years. Facebook was launched initially in 2004 for Harvard University members but has since expanded to over 34m users worldwide. MySpace, which was set up in 2003, has over 200m users and was bought by Rupert Murdoch's News Corporation in 2005 for $580m.
Previous research has suggested that a person's conventional friendship group consists of around 150 people, with five very close friends but larger numbers of people who we keep in touch with less regularly. This figure is so consistent that scientists have suggested it is determined by the cognitive constraints of keeping up with large numbers of people. But Dr. Reader and his team have found that social networking sites do allow people to stretch this figure. The team asked over 200 people to fill in questionnaires about their online networking, asking for example how many online friends they had, how many of these were close friends and how many they had met face to face. The team found that although the sites allowed contact with hundreds of acquaintances, as with conventional friendship networks, people tend to have around 5 close friends. Also, 90% of contacts that the subjects regarded as close friends were people they had met face to face. "People see face to face contact as being absolutely imperative in forming close friendships," added Dr. Reader. He told the British Association Festival of Science in York that social networking sites allow people to broaden their list of nodding acquaintances because staying in touch online is easy. "What social network sites can do is decrease the cost of maintaining and forming these social networks because we can post information to multiple people," he said.