Scientists have learned a great deal in the last thirty years by studying people as they sleep. They study the bodily characteristics that change during sleep. They have learned that there is one kind of sleep which causes rapid eye movement ( REM ) and another kind with no rapid eye movement (NREM).

Sleep is divided into three stages. In stage one, when you start to go to sleep, you have a pleasant floating feeling. In stage two, you sleep more deeply, and a noise will probably not wake you up. In stage three, the brain waves are less active. This third stage is when you dream, REM tends to signal that we are dreaming. For the rest of the night, you alternate between REM and NREM sleep.

Sleep is a biological need, but your brain never really sleeps. The things that are on your mind during the day are still there at night. They appear as dreams. Researchers say that normal people may have four or five REM periods of dreaming each night. The first one may begin only a half hour after they fall asleep, and the final one may last up to an hour. Nightmares (a frightening dream) usually happen toward the early morning.

Besides dreaming, snoring is also common in one's sleep. People snore because they have trouble breathing while they are asleep. Some snorers have a condition called apnea. They stop breathing up to thirty or forty times an hour because the muscles relax too much and block the airway. After a period of time, the brain will signal the person to start breathing again. During this time a person will snore. This is a dangerous condition, because once the brain is without oxygen for four minutes there could be serious brain damage. Sleep apnea can also cause irregular heartbeats, high blood pressure, and a general lack of energy.

What should you do if you have trouble sleeping? Lots of people take sleeping pills, but these are dangerous because they can be addictive. Doctors say the best thing is to try to relax and to avoid bad habits.

Sleep is important to humans. In an average lifetime, 220, 000 hours are spent sleeping, so we need to understand everything we can about sleep. Sweet dreams!

【1】Sleep is a(an) ________ need for humans.

A. emotional B. mental

C. biological D. psychological

【2】Which of the following conditions is NOT caused by sleep apnea?

A. A heart attack.

B. A lack of energy.

C. Irregular heartbeats.

D. High blood pressure.

【3】We can learn from the article that ____________.

A. our brains can get a good rest when we are asleep

B. it's impossible to stop the habit of taking sleeping pills

C. REM and NREM are ways to see if people are in a deep sleep.

D. in stage two people will probably not wake up if they hear a noise.

【4】Where is the article probably from?

A. A sports guidebook.

B. A health magazine.

C. A fashion website.

D. A news report.

【答案】

【1】C

【2】A

【3】D

【4】B

【解析】

试题分析：本文属于科普说明文，主要介绍人类的睡眠分为三个阶段以及这三个不同的阶段的特点。

【1】C 细节理解题。根据第三段第一句Sleep is a biological need, but your brain never really sleeps.可知睡眠是一种生理需要。故C正确。

【2】A 细节理解题。根据第四段最后一句Sleep apnea can also cause irregular heartbeats, high blood pressure, and a general lack of energy.可知呼吸暂停会导致心律不齐，高血压和精力不足。A项并没有提及。故A正确。

【3】D 细节理解题。根据第二段第三句In stage two, you sleep more deeply, and a noise will probably not wake you up.可知在睡眠的第二阶段，你睡得更深。噪音也无法把你吵醒。故D项说法正确。

【4】B 推理判断题。本文属于科普说明文，主要介绍人类的睡眠问题以及睡眠的不同阶段的特点。最可能是从健康杂志上摘录而来，不可能是时尚网站、新闻报道和运动指导。故B正确。