单项选择题
A．To make a comparison between the past and the present. B．To honor her father. C．To criticize the past. D．To criticize the present.
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