单项选择题
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
A．feeling of hatred B．power struggle C．that they don’ t care for each other D．that they may appeal to divorce