I. Cloze Test: for (1) to (19), choose one best answer from the box below; for (a), fill in theblank. (20%)           In 1965, 17-year-old high school student, Randy Gardner, stayed awake for 264 hoursto see how he coped without sleep. On the second day, he’s eyes stopped focusing. Next, helost the ability to__ (1)__ objects by touch. By day three, Gardner was moody anduncoordinated. At the end of the experiment, he was struggling to concentrate, had troublewith short-term memory, became paranoid, and started hallucinating. (a)Gardner recovered without long-term psychological or physical damage, for others, losingshuteye can result in hormonal __(2)__ , illness and, in extreme cases, death.        We’re only beginning to understand why we sleep to begin with, but we do know it’sessential. Adults need seven to eight hours a night, and adolescents need about ten. Wegrow sleepy due to signals from our body telling our brain we are tired, and signals from theenvironment telling us it's dark outside. The __(3)__ in sleep-inducing chemicals, like adenosineand melatonin, send us into a light__(4)__ that grows deeper, making our breathing and heartrate slow down and our muscles relax. This non-REM sleep is when DNA is repaired and ourbodies__ (5)__ themselves for the day ahead.         In the United States, it's estimated that 30% of adults and 66% of adolescents areregularly sleep-deprived. This isn't just a minor__ (6)__ . Staying awake can cause serious bodilyharm. When we lose sleep, learning, memory, mood, and reaction time areaffected. Sleeplessness may also cause inflammation, hallucinations, high blood pressure, andit's even been linked to diabetes and obesity. In 2014, a__ (7)__ soccer fan died after stayingawake for 48 hours to watch the World Cup. While his untimely death was due to astroke, studies show that __(8)__ sleeping fewer than six hours a night increases stroke risk byfour and half times compared to those getting a__ (9)__ seven to eight hours of shuteye. For ahandful of people on the planet who carry a rare inherited genetic mutation, sleeplessness is adaily reality. This __(10)__ , known as Fatal Familial Insomnia, places the body in a nightmarishstate of wakefulness, forbidding it from entering the __(11)__ of sleep. Within months oryears, this__ (12)__ worsening condition leads to dementia and death.         How can sleep deprivation cause such __(13)__ suffering? Scientists think the answer lieswith the accumulation of waste products in the brain. During our waking hours, our cells arebusy using up our day's energy sources, which get broken down into various__ (14)__ , including- 2 -adenosine. As adenosine builds up, it increases the __(15)__ to sleep, also known as sleeppressure. In fact, caffeine works by blocking adenosine's receptor pathways. Other wasteproducts also build up in the brain. If they're not cleared away, they collectively overload thebrain and are thought to lead to the many negative symptoms of sleep deprivation.        So, what's happening in our brain when we sleep to prevent this? Scientists foundsomething called the lymphatic system, a clean-up mechanism that removes this buildup andis much more active when we're asleep. It works by using cerebrospinal fluid to__ (16)__ awaytoxic byproducts that accumulate between cells. Lymphatic vessels, which__ (17)__ as pathwaysfor immune cells, have recently been discovered in the brain, and they may also play a role inclearing out the brain's daily waste products. While scientists continue exploring therestorative __(18)__ behind sleep, we can be sure that slipping into __(19)__ is a necessity if wewant to maintain our health and our sanity.  (AB) byproducts (AC) mechanisms (AD) condition(AE) consistent (BC) chronically(BD) devoted (BE) doze (CD) flush(CE) identify (DE) inconvenience(ABC) imbalance(ABD) immense (ABE) replenish (BCD) rise (BCE) sanctuary(BDE) serve (CDE) slumber (ABCD) progressively (ABCE) urge
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