Which are human systems?
a the amazon rain forest
i the appalachian trail
the george washington bridge
the himalayas
the hoover dam
the north american free trade agreement
the san andreas fault
the suez canal

it will be anything that is not made by nature, but by men. forests are not, mountains as well. not the fault either

radiative zone

explanation    

radiative zone is the layer of the sun which energy is transferred away from the core by radiation. although, the core is the only part of the sun that produces an appreciable amount of heat through fusion. in fact, 99% of the energy produced by the sun takes place within 24% of the sun's radius.