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

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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

单项选择题

By “just the tip of the iceberg” (Line 2, Para. 8), Siegel suggests that _________.

A．half-brain sleep has something to do with icy weather
B．the mystery of half-brain sleep is close to being solved
C．most birds living in cold regions tend to be half sleepers
D．half-brain sleep is a phenomenon that could exist among other species

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