You have noticed that your 84-year-old great-grandmother has a much smaller set of friends than she used to have. You know that the same individuals who she used to be friends with are still living in the same neighborhood. According to Cartensen's socioemotional selectivity theory, why is your grandmother not interacting with some of these old friends Older adults tend to .

a) become increasingly nervous around other older people

b) withdraw from friendships that are not rewarding

c) not care about friends any longer

d) become more reclusive