Caffeine and other stimulants cannot overcome the effects of severe sleep deprivation.

without harmful side effects, and it （） a wealth of nutrients.Yet, when most people drink coffee, they are not thinking that the beverage is （） their health.In fact, some may even feel a little guilty, （） some believe coffee isn’t good for you at all.

Well, coffee, like anything else, can cause problems if too much is （）.Moderate consumption of coffee （） your body with a wealth of antioxidants.These substances are responsible （） eliminating free radicals.They are the chemical byproducts produced any time your body does something.A small number of them can help serve （） a buffer against negative elements, if they aren’t （） in check.They can cause health problems.Antioxidants ensure that this doesn’t happen.

The psychological effects of caffeine cannot be（）either.Not only does caffeine make you more （）, but it can actually affect your mood.If you were feeling （） or overwhelmed, a nice cup of coffee could change your （）.The stack of work that seemed impossible before isn’t even a problem now.

（）, caffeine helps stimulate creativity as it speeds up the body’s functioning.That’s why coffee is often （） with writers and other intellectual professions.Other drugs （） to make people dumber.Consider what happens when people get high off of crack or when they get drunk off of alcohol.They won’t be （） at all.But with coffee, an individual gets a creative boost （） still helping their bodies.

In conclusion, don’t feel bad when you’re brewing your morning cup of coffee.（） a can of soda or a shot of alcohol, coffee will make you feel wonderful while keeping you healthy.Just remember, you do have to consume the beverage in （）.

1.A.cleanB.clarityC.brightnessD.clear

2.A.combinesB.contentsC.consistsD.contains

3.A.improvingB.harmingC.threateningD.stimulating

4.A.andB.butC.sinceD.while

5.A.consumedB.conductedC.engagedD.attracted

6.A.providesB.attributesC.absorbsD.attaches

7.A.withB.ofC.forD.to

8.A.forB.forC.toD.with

9.A.takenB.madeC.putD.kept

10.A.ignoredB.abandonedC.deletedD.canceled

11.A.sternB.shrewdC.alertD.nasty

12.A.immersedB.depressedC.oppressedD.compelled

13.A.interpretiveB.relativeC.representativeD.perspective

14.A.On the contraryB.On the other handC.In additionD.At last

15.A.associatedB.connectedC.coincidedD.compared

16.A.intendB.tendC.extendD.pretend

17.A.deliberateB.credibleC.accurateD.functional

18.A.thoughB.whileC.beforeD.until

19.A.LikeB.WhetherC.EitherD.Unlike

20.A.moderationB.particularC.meditationD.standard

A.strengthen

B.submit

C.overpower

D.defeat

Late-night Drinking

Coffee lovers beware. Having a quick "pick-me-up" cup of coffee late in the day will play havoc with your sleep. As well as being a stimulant, caffeine interrupts the flow of melatonin, the brain hormone that sends people into a sleep.

Melatonin levels normally start to rise about two hours before bedtime. Levels then peak between 2 am and 4 am, before falling again. "It's the neurohormone that controls our sleep and tells our body when to sleep and when to wake," says Maurice Ohayon of the Stanford Sleep Epidemiology Research Center at Stanford University in California. But researchers in Israel have found that caffeinated coffee halves the body's levels of this sleep hormone.

Lotan Shilo and a team at the Sapir Medical Center in Tel Aviv University found that six volunteers slept less well after a cup of caffeinated coffee than after drinking the same amount of decaf. On average, subjects slept 336 minutes per night after drinking caffeinated coffee, compared with 415 minutes after decal They also took half an hour to drop off — twice as long as usual — and jigged around in bed twice as much.

In the second phase of the experiment, the researchers woke the volunteers every three hours and asked them to give a urine sample. Shilo measured concentrations of a breakdown product of melatonin. The results suggest that melatonin concentrations in caffeine drinkers were half those in decal drinkers. In a paper accepted for publication in Sleep Medicine, the researchers suggest that caffeine blocks production of the enzyme that drives melatonin production.

Because it can take many hours to eliminate caffeine from the body, Ohayon recommends that coffee lovers switch to decaf after lunch.

The author mentions "pick-me-up" to indicate that

A．melatonin levels need to be raised.

B．neurohormone can wake us up.

C．coffee is a stimulant.

D．decaf is a caffeinated coffee.

some estimates, over 30% of all adults in the world drink coffee at least once a day on the average. Coffee contains a kind of drug called caffeine. (66) Caffeine is a chemical substance that stimulates the nerves of the body. Drinking coffee tends to make people a little bit more awake, —at least for a short time—because of this stimulating effect on the nervous system. A cup of coffee has, on the average, about 3% caffeine in it.

One story of the discovery of the coffee plant relates to this effect of caffeine. According to the story, coffee was discovered in East Africa. The story says that coffee was first found by a goat farmer named Kaldi. This was about the year 850.

Kaldi was leading his animals through the mountains and the goats were stopping repeatedly to eat the plants near the path. Suddenly, some of the goats started jumping up and down in a very strange way.

Kaldi figured out that the goats were acting this way because of the plants they were eating. Kaldi himself tried eating some of the green beans that the goats had been eating. He, too, felt the stimulating effect of the beans.

Kaldi wanted to prove what had happened, so he picked some of the beans and took them back to his home village, where he told his story. The green bean got the name "Kaffa" and later "coffee" because the beans were discovered in a place called Kaffa in Africa.

Then for years, people used to eat a few of the green Kaffa beans when they were in the mountains and needed extra energy or stimulation. It was later found that the coffee beans could be picked and then dried until they turned brown, and then they could be stored. If the beans were dried and stored, they could be used at any time.

Caffeine is a kind of drug that can______.

A．strengthen one's heart

B．make one's bones strong

C．make one more active or alert

D．ease the pain on the body

A．Many？extracellular？signals？acting？via？GPCRs？affect？the？activity？of？the？enzyme？adenylyl？cyclase？and？thus？alter？the？intracellular？concentration？of？the？second？messenger？molecule？cyclic？AMP.

B．Most？commonly,？the？activated？G？protein？α？subunit？switches？on？the？adenylyl？cyclase,？causing？a？dramatic？and？sudden？increase？in？the？synthesis？of？cyclic？AMP？from？ATP.

C．To？help？terminate？the？signal,？a？second？enzyme,？called？cyclic？AMP？phosphodiesterase,？rapidly？converts？cyclic？AMP？to？ordinary？AMP.？Cyclic AMP phosphodiesterase is continuously active inside the cell. Because it eliminates cyclic AMP so quickly, the cytosolic concentration of this second messenger can change rapidly in response to extracellular signals, rising or falling tenfold in a matter of seconds.

D．Cyclic AMP is water-soluble,so it can, in some cases, carry the signal throughout the cell, traveling from the site on the membrane where it is synthesized to interact with proteins located in the cytosol, in the nucleus, or on other organelles. One？way？that？caffeine？acts？as？a？stimulant？is？by？inhibiting？this？phosphodiesterase？in？the？nervous？system,？blocking？cyclic？AMP？degradation？and？thereby？keeping？the？concentration？of？this？second？messenger？high.

. During vigorous exercise, our muscles tire as they run out of fuel and build up waste products. Muscle performance can also be affected by a phenomenon called "central fatigue," in which an imbalance in the body's chemical messengers prevents the central nervous system from directing muscle movements effectively. It was not known, however, whether central fatigue might also affect motor systems not directly involved in the exercise itself—such as those that move the eyes. To find out, researchers gave 11 volunteers a carbohydrate solution either with a moderate dose of caffeine—which is known to stimulate the central nervous system—or as a placebo without, during 3 hours of cycling. After exercising, the scientists tested the cyclists with eye-tracking cameras to see how well their brains could still control their visual system. The team found that exercise reduced the speed of rapid eye movements by about 8%, preventing their ability to capture new visual information. The caffeine—the equivalent of two strong cups of coffee—was sufficient to counteract this effect, with some cyclists even displaying increased eye movement speeds, the team reports today in Scientific Reports. So it might be a good idea to get someone else to drive you home after that marathon.

will have come closer to cultural harmony.

A、one and the other’s

B、each and the other’s

C、one another’s

D、the one’s and the other’s

A.the other

B.the others

C.other

A.other ​

B.theother

C.another

D.other’s