A、Obsession with alcohol. B、Low blood pressure. C、Low spirits. D、Working conditions. C原文中提到，调研者说压力、焦虑以及情绪低落是造成睡眠差的罪魁祸首。因此答案为C。

Many young people struggle to get a good night’s sleep which could be harming their health, according to the results of a major survey published to mark World Sleep Day.
    The Sleep Research Society surveyed nearly 60000 people aged 10 to 45, and found that 91％ of them reported "not having enough sleep" or "still being tired after sleep. " Only about 5. 6％ of respondents said they felt energetic after sleep. About three quarters of respondents said they experienced difficulty falling asleep, and 13％ said they really struggled to fall asleep. Only about 11％ said they could sleep through the night without waking up.
    Many respondents cited work pressure as a major influence on their sleep quality, and could lead to bad sleep.
    The survey showed 60％ of the respondents would choose to work instead of sleep.
    In general, people with good education background tended to be more self-disciplined about getting enough sleep, but only 5％ of respondents had a routine daily schedule.
    Sleep problems have little direct link to income, working conditions or social status, according to the survey.
    "The portion of people with bad sleep is almost the same in different social layers, " the report stated.
    Surveyors said that stress, anxiety, and low spirits were the main culprits in bad sleep, worsened by the obsession with electronic products that could cause blue light effects disrupting sleep.
    Some 93％ said they would play with smartphones before sleep, watching TV series or shopping online.
    Surveyors believed that the random life schedules would lead young people to have low work efficiency, low appetite but higher cancer risk.
    Questions 12 to 15 are based on the passage you have just heard.
    12. What did the Sleep Research Society find through their survey?
    13. What kind of people tended to be more self-disciplined about getting enough sleep according to the survey?
    14. Which was a main cause of bad sleep according to the surveyors?
    15. What may be the result of random life schedules for young people?