单项选择题
A．study its importance in war B．study its volcanoes C．enjoy its freezing weather D．enjoy its beauty of nature
A．television B．radio C．computer D．the writer
A．Getting off to work with a minimum effort helps save one’s energy. B．Dr. Kleitman explains why people reach their peak at different hours of day. C．Habit helps a person adapt to his own energy cycle. D．Children have energy cycles, too.