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

According to the passage, birds often half sleep because _________.

A．they have to watch out for possible attacks
B．their brain hemispheres take turns to rest
C．the two halves of their brain are differently structured
D．they have to constantly keep an eye on their companions

单项选择题

Reebok's view that “consumers judge the quality of the brand by the quality of its distribution” (Line 5, Para. 2) implies that ________.

A．the quality of a brand is measured by the service quality of the store selling it
B．the quality of a product determines the quality of its distributors
C．the popularity of a brand is determined by the stores that sell it
D．consumers believe that first-rate products are only sold by high-quality stores

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