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 a.m. and 4 a.m., 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 decaf. They also took half an hour to drop off4—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 decaf drinkers. In a paper accepted for publication in Sleep Medicinc, 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.

1．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.

2. Which of the following tells us how caffeine affects sleep?
  A. Caffeine blocks production of the enzyme that stops melatonin production.
  B. Caffeine interrupts the flow of the hormone that prevents people from sleeping.
  C. Caffeine halves the body’s levels of sleep hormone.
  D. Caffeine stays in the body for many hours.

3. What does paragraph 3 mainly discuss?
  A. Different effects of caffeinated coffee and decaf on sleep.
  B. Different findings of Lotan Shilo and a team about caffeine.
  C. The fact that the subjects slept 415 minutes per night after drinking decaf.
  D. The evidence that the subjects took half an hour to fall asleep.

4.What does the experiment mentioned in paragraph 4 prove?
  A. There are more enzymes in decaf drinkers’ urine sample.
  B. there are more melatonin concentrations in caffeine  drinkers’ urine sample.
  C. Decaf drinkers produce less melatonin.
  D. Caffeine drinkers produce less sleep hormone.

5. The author of this passage probably agrees that
  A. coffee lovers sleep less than those who do not drink coffee.
  B. we should not drink coffee after supper.
  C. people sleep more soundly at midnight than at 3 a.m.
  D. if we feel sleepy at night, we should go to bed immediately.
Pool Watch
      Swimmers can drown in busy swimming pools when lifeguards fail to notice that they are in trouble. The Royal Society for the Prevention of Accidents says that on average 15 people drown in British pools each year, but many more suffer major injury after getting into difficulties. Now a French company has developed an artificial intelligence system called Poseidon that sounds the alarm when it sees someone in danger of drowning.
      When a swimmer sinks towards the bottom of the pool, the new system sends an alarm signal to a poolside monitoring station and a lifeguard’s paper. In trials at a pool in Ancenis, near Nantes, it saved a life within just a few months, says Alistair MeQuade, a spokesman for its maker, Poseidon Technologies.
      Poseidon keeps watch through a network of underwater and overheard video cameras. AI software analyses the images to work out swimmers trajectories. To do this reliably, it has to tell the difference between a swimmer and the shadow of someone being cast onto the bottom or side of the pool. “The underwater environment is a very dynamic one, with many shadows and reflections dancing around.” Says McQuade.
      The software does this by “projecting” a shape in its field of view onto an image of the far wall of the pool. It does the same with an image from another camera viewing the shape from a different angle. If the two projections are in the same position, the shape is identified as a shadow and is ignored. But if they are different, the shape is a swimmer and so the system follows its trajectory.
      To pick out potential drowning victims, anyone in the water who starts to descend slowly is added to the software’s “pre-alert” list, says McQuade. Swimmers who then stay immobile on the pool bottom for 5 seconds or more are considered in danger of drowning. Poseidon double-checks that the image really is of a swimmer, not a shadow, by seeing whether it obscures the pool’s floor texture when viewed from overhead. If so, it alerts the lifeguard, showing the swimmer’s location on a poolside screen.
      The first full-scale Poseidon system will be officially opened next week at a pool in High Wycombe. Buckinghamshire. One man who is impressed with the idea is Travor Baylis, inventor of the clockwork radio. Baylis runs a company that installs swimming pools—and he was once an underwater escapologist with a circus. “I say full marks to them if this works and can save lives,” he says. But he adds that any local authority spending £30,000-plus on a Poseidon system ought to be investing similar amounts in teaching children to swim.

1. AI means the same as
  A. an image.                                         
  B. an idea.
  C. anyone in the water.                         
  D. artificial intelligence.

2. What is required of AI software to save a life?
  A. It must be able to swim.
  B. It must keep walking round the pool.
  C. It can distinguish between a swimmer and a shadow.
  D. It can save a life within a few months.

3. How does Poseidon save a life?
  A. He plunges into the pool.             
  B. It alerts the lifeguard.
  C. He cries for help.                                 
  D. It rushes to the pool.

4. Which of the following statements about Trevor baylis is NOT true?
  A. He runs.
  B. He invented the clockwork radio.
  C. He was once an entertainer.
  D. He runs a company.

5. The word “considered” in paragraph 5 could be best replaced by
  A. “thought”.              B. “rated”.          C. “regarded”.                  D. “believed”.