15. How were Troubadours crucial in communication during the Middle Ages?

I dont know

Explanation:

how important were they

question

which are human systems?

the amazon rain forest

the appalachian trail

the george washington bridge

the himalayas

the hoover dam

the north american free trade agreement

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.