Complex sentence: Regenerative cooling in rockets is where some or all of the propellant is passed through tubes, channels or otherwise in a jacket around the combustion chamber or nozzle to cool the engine becasue the fuel in particular and sometimes the oxidiser are good coolants.
Split into simpler sentences: Regenerative cooling in rockets is where some or all of the propellant is passed through tubes, channels or otherwise in a jacket around the combustion chamber or nozzle to cool the engine. The fuel in particular and sometimes the oxidiser are good coolants.