Especially if you breathe air, it's very hard to get from planet A to planet B, because there's no air in between. But if you breathe air --  -- you're dead --  -- as soon as you're off the planet, unless you have a spaceship.
诸多难题，比如空气 所以说这样的旅途是很困难的 你在途中是没有空气的  你会死的  只要你离开了地球，除非你去到太空船里头