A、Friends should be willing to sacrifice and never ask for rewards. B、There should be no secrets between friends. C、Friends shou

　　With growing numbers of people living alone, either by choice or circumstance, friendships can occupy the emotional space that other people fill with spouses or significant others. Friends can link us to broader social networks and help enrich our lives. (20) Friendships are what make us unique human. There is no other species that interacts so widely with other members of their species. Solid friendships provide needed validation that a person is valuable and of interest to other people. Relationships help people feel that they’re worthy, that they are capable, that they can set goals and accomplish them, and that they can control their life. (21) Friendships could be represented by three concentric circles as very close, close, and not-so-close but still meaningful personal ties. A person’s inner circle usually includes close family members and friends who are thought of as family. Close friendships display strong support and affection. A close friend who listens and pays attention to you, is willing to help you, and has shared interests. There is give-and-take and often a balance that doesn’t put too much weight on one party. (22) Developing and maintaining friendships requires continuous attention. Give-and-take is important. Other elements of solid friendships include paying attention to what’s going on in a friend’s life, seeking out some shared interests and participating in activities together, and being able to confide deeply to a friend.
　　20. Why does the speaker say friendships are unique to human beings?
　　21. What can we learn about the friendship circles?
　　22. What should friends do to maintain a friendship?