Read the following passage and blacken the letter A, B, C or D on your answer sheet to indicate the correct word for each of the blanks in the following question. 

Why is it that many teenagers have the energy to play computer games until late at night but can't find the energy to get out of bed in time for school? According to a new report, today's generation of children are in danger of getting so (20) _______ sleep that they are putting their mental and physical health at risk. Adults can easily survive on seven to eight hours' sleep a night, (21) _____teenagers require nine or ten hours. According to medical experts, one in five youngsters gets anything between two and five hours' sleep a night less than their parents did at their age. 

This (22) ______ serious questions about whether lack of sleep is affecting children's ability to concentrate at school. The connection between sleep deprivation and lapses in memory, impaired reaction time and poor concentration is well (23) _________. Research has shown that losing as little as half an hour's sleep a night can have profound effects on how children perform the next day. A good night's sleep is also crucial for teenagers because it is while they are asleep (24) they release a hormone that is essential for their 'growth spurt' (the period during teenage years when the body grows at a rapid rate. It's true that they can, to some extent, catch up on sleep at weekends, but that won't help them when they are dropping off to sleep in class on a Friday afternoon.