點解太空船的火箭有三層和兩層，每層有什麼作用？

it is because it can provide extra pushing force during lift-off and
when the fuels of the second stage is used up,
it dropped to reduce the weight of the rocket

The top (sharp) stage is for holding the astronouts(太空人); the middle stage is for holding the fuel(燃料) and the lower stage is for holding the pusher (推進器). Why the need to be seperatted(分隔)?It is for the safty of the astronouts(太空人). If the rocket have any problems the astronouts can leave the tp stage alone. Also the stage will leave away while flying.