单项选择题

While sleeping, some water mammals tend to keep half awake in order to______.

A．alert themselves to the approaching enemy
B．emerge from water now and then to breathe
C．be sensitive to the ever-changing environment
D．avoid being swept away by rapid currents

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单项选择题

The new trend in artificial intelligence research stems from

A．the shift of the focus of study on to the recognition of the shapes of objects
B．the belief that human intelligence cannot be duplicated with logical, step-by-step programs
C．the aspirations of scientists to duplicate the intelligence of a ten-month-old child
D．the efforts made by scientists in the study of the similarities between transistors and brain cells

单项选择题

The example of a bird sleeping in front of a mirror indicates that______.

A．the phenomenon of birds dozing in pairs is widespread
B．BI birds prefer to sleep in pairs for the sake of security
C．even an imagined companion gives the bird a sense of security
D．a single pet bird enjoys seeing its own reflection in the mirror

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