请先阅读下面短文，掌握其大意，然后从各小题所给的A、B、C、D四个选项中选出可以填入相应空白处的最佳选项，并在答题卡上将该项涂黑。Getting Your Sleep Cycle (周期) Right
Warning: this article may make you want to yawn (打哈欠). Why? It's because we're looking into the world of sleep cycles.
Our bodies sleep in 90-minute cycles, experiencing five to six each 1 . At first, you enter a light stage (阶段) of sleep when your muscles (肌肉) 2 . Then, the body temperature drops, and the heart beat slows.
Next comes 3 sleep. It's difficult to wake up this stage. This is when your body repairs 4 and builds up energy (能量) for the day ahead. 5 , you get into the rapid eye-movement (REM，快速眼动) sleep stage. It is when most dreaming happens. 6 REM sleep, the cycle repeats.
Waking up in the morning in the "wrong" stage can make you feel especially 7 . An app called Sleep Calculator can help you avoid this. It's a tool made to work out the 8 bedtime for you based on your wake-up time.
Developed by the UK company Hillarys, this smart calculator considers the 9 cycles our bodies go through each night. Whether you're an early bird or a night owl (猫头鹰), simply input your wake-up time , 10 the calculator will work its magic, suggesting the perfect bedtime to make sure that you 11 and shine with a spring in your step.
It's also worth noting that you shouldn't just 12 your sleep cycle whenever you want. Many young people go to bed 13 and get up late, such as sleeping from 2 a.m. to 10 a.m. They 14 as long as they have 8 hours of sleep, everything will be fine.
But in fact, our bodies can tell the 15 , especially by using light and temperature. If we wake up too late, we may feel a bit like a zombie (僵尸). That's why sometimes we feel even more tired after oversleeping.
