单项选择题
A．demanding greater freedom to go wherever they please B．making decisions without parental interference C．getting married whenever they please D．doing what they please
A．a medical operation B．a medical needle C．a medical technique D．a medical machine
A．Because small pieces of food would fall down to the floor. B．Because weightless pieces of food might make trouble when they travel around. C．Because they haven’ t enough food for longer trips. D．Because astronauts don’ t want to waste foo