单项选择题
A．threatened B．claimed C．explored D．narrowed
A．half-brain sleep is found in all kinds of birds B．half-brain sleep is characterized by accelerated brain waves C．birds can control their half-brain sleep consciously D．birds always sleep with the whole of their brain at rest
A．some kind of disaster a person experienced in his childhood B．a vague sense that something will happen and it does happen later C．the prediction of the death of a close friend D．uncertainty about an impending accident