How would you like to sleep with one half your brain asleep and the other half awake? Dolphins sleep this way. Recently , scientists at Indiana State University have discovered that ducks sleep this way too. They found that ducks sleep half awake so they can rest and watch for danger at the same time.

After putting their ducks in a row and videotaping them, some researchers found ducks on the end of each row spent more time asleep with one eye open ,apparently looking for predators.

“The more the ducks felt threatened ,the more they slept with one eye open,” said lead author Niels C. Rattenborg ,a graduate student at Indiana State University ,Terre Haute .”the unique aspect is not that they do it ,but that they control it . When they sleep at the edge of a group ,they tend to realize greater danger ,so they spend more time sleeping with one half of their brain.” Ducks with one eye open were still awake enough to detect predators ,said the authors of the study ,which appears today in the journal Nature.

 The researchers studied four groups of four ducks held in plastic boxes ,which were arranged in a row .Ducks on the end were found to sleep with one eye open 31.8 per cent of the time, compared to 12.4 percent of the time for ducks in the central position.

Also ,ducks in the central position did not open one eye more than the others, while ducks on each end kept the eye facing away from the group open 86.2 per cent of the time. Brain wave readings of the ducks showed that the half of the brain receiving signals from the closed eye indicated that half of the brain was sleeping. Signals from the half of the brain receiving signals from the open eye showed a state between fully awake and asleep.

71．It was discovered that      .

       A．most people would like to be half asleep

       B．ducks can sleep half awake

       C．dolphins sleep on their way

       D．ducks have different sleeping habits from each other

72．A predator is most likely to be       .

       A．an animal that hunts ,kills and eats other animals

       B．a human being who looks after and feeds ducks

       C．a scientist who does research work on animals

       D．an animal that is likely to be friends with ducks

73．Ducks at the end of each row sleep with one eye open because    .

       A．they are looking for food                     

       B．they want to enjoy the scenery

       C．they are watching out for danger          

       D．they are unique in their sleeping habit

74．How many ducks were used in the experiment?

       A．Four.                  B．Eight.                  C．Twelve.               D．Sixteen.

75．Which of the following is true according to the passage?

       A．Ducks on the northern end of a row would keep their eye facing the south open.

       B．Ducks with less sense of duty usually choose to stay in the center of a row.

       C．Ducks with one eye open at the edge can still enjoy a certain degree of sleep.

       D．A video tape recorder was the only electronic device used in the experiment.