space is a vacuum & vaccum does not contain oxygen ->  there is no oxygen in space  a human is a kind of animal & an astronaut is a kind of human ->  an astronaut is a kind of animal  an astronaut is a kind of animal & an animal requires oxygen to breathe ->  an astronaut requires oxygen to breathe  there is no oxygen in space & an astronaut requires oxygen to breathe & spacesuit backpacks contain oxygen -> an astronaut requires the oxygen in a spacesuit backpack to breathe