A、By telephone. B、By means of questionnaire. C、By letter. D、By e-mail. A信息明示题。短文中明确提到，盖洛普咨询公司于2008年以电话方式对34万多成年人进行了调查。

Old age may not sound exciting. But recent findings offer good news for older people and for people worried about getting older. Researchers found that people become happier and experience less worry after they reach the age of 50. The findings came from a survey of more than 340 000 adults in the United States.(29)The Gallup Organization questioned them by telephone in 2008. At that time, the people were between the ages of 18 and 85. The researchers asked questions about emotions like happiness, sadness and worry. They also asked about mental or emotional stress. Arthur Stone in the Department of Psychiatry and Behavioral Science at Stony Brook University in New York led the study. The findings showed that levels of stress were highest among adults between the ages of 22 and 25, but stress levels dropped sharply after people reached their 50s.(30)Happiness was highest among the youngest adults and those in their early 70s. The study also showed 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. Researchers say they do not know why happiness increases as people get older. One theory is that, as people grow older, they grow more thankful for what they have and have better control of their emotions. They also spend less time thinking about bad experiences.(31)Prof. Stone says the emotional patterns could be linked to changes in how people see the world, or maybe even changes in brain chemistry.
29. How did the Gallup Organization conduct the survey?
30. Which of the following group seems happiest according to the passage?
31. Why does happiness increase as people get older according to Prof. Stone?