Why do long-distance aircraft choose to fly in the lower part of later troposphere​

Aregion is an area of land that has common features. these features can be natural, such as climate or landscape. they can also be artificial, such as language or religion. the xinjiang uyghur autonomous region, above, is an area of china inhabited by uyghurs, a muslim group with ethnic ties to turkish people.

Answer primary waves;

Answergoogle earth; i believe this is the correct answer, plz check first;