Prominent among theories of the function of sleep is Meddis’ immobilization hypothesis, which holds that sleep, rather than serving a restorative function, plays a protective role during times that animals cannot be usefully engaged in other activities. Meddis reasoned that animals not immediately threatened by predators would be safer if they passed the time sleeping.

　　However, that hypothesis cannot easily explain why one often observes a rebound in sleep time or intensity following a period of sleep deprivation. Neither does the hypothesis explain the existence of various states of sleep, which themselves may be associated with different functions.

　　Consider each of the choices separately and select all that apply.

　　1. According to the passage, the immobilization hypothesis fails to account for which of the following facts?

　　A. That sleep does not appear to be a uniform and unchanging state

　　B. That under certain conditions animals appear to need more sleep than usual

　　C. That animals rarely sleep when a predator has been detected nearby

　　2. In the context of the passage as a whole, the highlighted portion serves primarily to

　　A. present the thinking that led scientists to qualify a widely accepted view

　　B. describe the basis on which a hypothesis was advanced

　　C. illustrate the kind of reasoning that is applied in a branch of science

　　D. explain how a hypothesis can be tested empirically

　　E. relate the analysis that refined a tentative explanation

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