A、We are busier. B、There are fewer social activities. C、More people like living alone. D、People are becoming more isolated. D

Thirty years ago, anyone blaming loneliness for physical illness would have been laughed at. But as scientists studied different populations, loneliness kept emerging as a risk factor. In one study, Californian researchers followed 4,700 residents of Alameda County for 10 years, starting in 1965.
    At first, the participants reported their key sources of companionship and estimated the time they devoted to each other. During the study, the people who reported the least social contact died at nearly three times the rate of those reporting the most. The source of companionship didn’t matter, but time spent with others was critical.
    Since then, researchers have studied men, women, soldiers and students from countries all over the world. And the same pattern keeps emerging. Women who say they feel isolated go on to die of cancer at several times the expected rate. College students who report "strained and cold" relationships with their parents suffer extraordinary rates of hypertension and heart disease decades later. Heart-attack survivors who happen to live by themselves die at twice tile rate of those who live with others.
    For those of us who are still healthy, the lesson should be obvious. It’s clear that reaching out to others can help our bodies thrive. It’s equally clear that we’re growing more isolated. In 1900, only 5 percent of U.S. households consisted of one person living alone. The proportion reached 13 percent in 1960, and it stands at 25 percent today. In a book entitled Bowling Alone, author Robert Putnam shows that oar social connections are disappearing on other levels, too In 1976, Americans attended an average of 12 club meetings a year. The current average is five. Card games, dinner parties and shared family meals have all followed the same pattern. We all have a good excuse we’re too busy but we shouldn’t be surprised when it catches up with us.