A、It did not examine teens’ use of smartphones. B、It proves the serious influence of social media on teen suicide. C、It involves

An increase in suicide rates among US teens occurred at the same time social media use surged. A new study suggests there may be a link.
    Suicide rates for teens rose between 2010 and 2015 after they had declined for neaily two decades, according to data from the federal Centres for Disease Control and Prevention (CDC). Why the rates went up isn’t known.
    The study’s authors looked at CDC suicide reports from 2009 to 2015 and results of two surveys given to US high school students to measure attitudes, behaviour and interests. About half a million teens aged from 13 to 18 were involved. They were asked about use of electronic devices, social media, print media, television and time spent with friends. Questions about mood included frequency of feeling hopeless and considering or attempting suicide.
    The researchers didn’t examine circumstances surrounding individual suicides. Dr. Christine Moutier said the study provides weak evidence for a popular theory about social media’s influence. She said many factors influence teen suicide.
    Nonetheless, the study highlighted interesting data about teens, their use of smartphones and social media, as well as their mental health.
    For example, the study showed that teens’ use of electronic devices, including smartphones, for at least five hours daily more than doubled. These teens were 70％ more likely to have suicidal thoughts or actions than those who reported one hour of daily use.
    “We need to stop thinking of smartphones as harmless, said study author Jean Twenge. Twenge said many will say, “ ’Oh, teens are just communicating with their friends. ’ Monitoring kids’ use of smartphones and social media is important, and so is setting reasonable limits. ”
    9. What can we learn about suicide rates for teens before 2010?
    10. What did Christine Moutier say about the new study?
    11. What did Jean Twenge say about smartphones and social media?