According to a recent survey, British teenagers are damaging  their health by not getting enough sleep because they are prevented from doing so by electronic gadgets   in their bedrooms. According to the Sleep Council, "junk sleep" could compete with eating unhealthy junk food as a main worrying lifestyle for parents of teenage children. Among the l, 000 students aged 12 t0 16 who were tested in the survey, 30 percent just slept for 4 to 7 hours a day. Almost a quarter said they fell asleep, more than once a week, while watching TV, listening to music or using other electronic gadgets. "This is a quite worrying trend ", said Dr Chris Idzikowski of the Edinburgh Sleep Centre. "What we are seeing is the appearance of terrible junk sleep - sleep that is of neither the length  nor the quality it should be." Nearly each of the teenagers had a phone, music system or TV in his or her bedroom, with around two-thirds owning all three. Almost one in five of the teenage boys said the quality of their sleep had been influenced by leaving their TVs or computers on. The survey also found that 40 percent of youngsters felt tired each day, with girls aged 15 to 16 feeling the worst. "Teenagers need to wake up to the fact that to perform  well. They need to do something about their sleep. I'm shocked  that so few teenagers have noticed ," said Idzikowski. Which of the following kinds of sleep is thought to be "junk sleep"?
A long sleep of good quality. A short but good sleep. A sleep with many dreams. A short sleep of low quality.