Please answer the following question: Write a multi-choice question for the following article, with the given choices and answer: Article: March 21 is World Sleep Day. How's your sleep recently? The Chinese Medical Doctor Association asked 8,200 people in China about their sleep. More than 36.3 percent of them said they often sleep badly. The study also finds that many students have only 5 hours of sleep a day. According to the US National Sleep Foundation, teenagers need 8.5 to 9 hours of sleep every night. What cuts into their sleeping time? Homework. Also, school starts early in the morning. But bad sleeping habits also play a role. Do you like to have a look at your mobile phone before going to bed? The survey finds that 60 percent of people check their phones before they sleep. They read news, check their WeChat or chat with QQ friends. It's important for us to get enough sleep. We feel tired and think slowly. Besides, sleepy kids are often unhappy, says a study by the US National Sleep Foundation. We can't change our school time. But there are still ways to get better sleep. Stay away from coke, coffee and tea at night. They make it hard to fall asleep. Watch less television. Leave your mobile phone and tablet computer on your desk. ,,. Options: A 5 to 6 hours. B 6 to 8 hours. C 8.5 to 9 hours. D 9 to 10 hours. Answer: C 8.5 to 9 hours. Question:
A:
How many hours should teenagers sleep every night according to the US National Sleep Foundation?