Coffee lovers, be careful. Having a quick “pick-me-up” cup of coffee late in the day will interrupt your sleep. As well as being a stimulant (兴奋剂)，caffeine interrupts the flow of melatonin (褪黑激素),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 (神经激素)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 (脱咖啡因咖啡).On average, subjects slept 336 minutes per night after drinking caffeinated coffee, compared with 415 minutes after decaf. They also took half an hour to drop off, twice as long as usual.
In the second phase of the experiment, the researchers woke the volunteers every three hours and asked them to give a urine (尿)sample. Shilo measured concentrations of a breakdown product of melatonin. The results suggest that melatonin concentrations in caffeine drinkers were half those in decaf drinkers. In a paper accepted for publication in Sleep Medicine，the researchers suggest that caffeine blocks production of the enzyme (酶) 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.
31 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 caffeine can balance our brain hormone
解析：文中第一段第二句提到 “Having a quick “pick-me-up” cup of coffee late in the day will interrupt your sleep”，说明在一天中的晚些时候喝一杯提神咖啡会影响睡眠。所以答案为 C。
32 Which of the following tells us how caffeine affects sleep?
A It blocks production of the enzyme that stops melatonin production.
B It interrupts the flow of the hormone that prevents people from sleeping.
C It halves the body’s levels of sleep hormone.
D It stays in the body for many hours.
解析：文中第二段最后一句提到 “But researchers in Israel have found that caffeinated coffee halves the body’s levels of this sleep hormone”，说明以色列研究界发现含咖啡因的咖啡使体内的褪黑激素减半，所以答案为C。
33 What does Paragraph 3 mainly discuss?
A Different effects of caffeinated coffee and decaf on sleep.
B Lotan Shilo’s research design on sleep.
C What the subjects did after drinking decaf at night.
D Why some subjects took half an hour to fall asleep.
解析：第三段介绍了 Lotan Shilo和他的小组发现六名自愿者在喝了含咖啡因的咖啡之后的睡眠质量比喝了不含咖啡因的咖啡之后要差，受试者在喝了含咖啡因的咖啡;平均每晚睡336分钟，而喝了不含咖啡因的咖啡后睡415分钟。所以，这段主要讲的是含咖啡因的咖啡与不含咖啡因的咖啡对睡眠的不同影响，答案是A。
34 The experiment mentioned in Paragraph 4 finds that caffeine drinkers______.
A sleep longer than decaf drinkers
B produce more urine at night
C wake up every three hours
D produce less melatonin
解析：文中第四段第二句提到 “The results suggest that melatonin concentrations in caffcinc drinkers were half those in decaf drinkers”，说明喝含咖啡因咖啡的人褪黑激素的浓度是喝 了不含咖啡因咖啡的人的一半，所以答案是D。
35 Ohayon advises coffee lovers ______.
A to take decaf after lunch
B to drink less coffee during the day
C not to go to bed after taking coffee
D not to drink coffee after supper
解析：文中第五段提到 “Ohayon recommcnds that coffce lovers switch to decaf after lunch”， 说明Ohayon建议爱喝咖啡的人午餐喝不含咖啡因的咖啡，因此答案是A。C全文都在讲芭蕾的发展历程。