A、18-21. B、22-25. C、30-50. D、70-80. B文中说：纽约州立大学石溪分校精神病学和行为科学系的Arthur Stone领导了这项研究。他的团队发现，年龄在22岁到25岁的成年人承受的压力最大。

People generally become happier and experience less worry after age fifty. The findings came from a Gallup Survey of more than three hundred forty thousand adults in the United States in two thousand and eight. At that time, the people were between the ages of eighteen and eighty-five.
    Arthur Stone in the Department of Psychiatry and Behavioral Science at Stony Brook University in New York led the study. His team found that levels of stress were highest among adults between the ages of twenty-two and twenty-five. Stress levels dropped sharply after people reached their fifties.
    Happiness was highest among the youngest adults and those in their early seventies. But the people least likely to report feeling negative emotions were those in their seventies and eighties. The survey also found that men and women have similar emotional patterns as they grow older. However, women at all ages reported more sadness, stress and worry than men did.
    The researchers also considered possible influences like having young children, being unemployed or being single. But they found that influences like these did not affect the levels of happiness and well-being related to age.
    So why would happiness increase with age? One theory is that, as people get older, they become more thankful for what they have and have better control of their emotions. They also spend less time thinking about bad experiences.
    Happiness is not the only thing that apparently improves with age. Another study surveyed more than one hundred and fifty thousand American adults. The original goal was to confirm the popular belief that aging is connected with increased sleep problems. The survey did find an increase during middle age, especially in women. But except for that, people reported that they felt their sleep quality improved as they got older.
Q10: Which age group has the highest stress level in the Gallup Survey?
Q11: Why would happiness increase with age?
Q12: Which was one of the findings of a second survey?