Ithink the answer is a.
which is most challenging for developing countries?
large aging populations economic and employment issues social and environmental issues outsourcing of jobs to nearby areas

Social and environmental issues

Explanation:

Developing economies are middle-income countries that have experienced high rates of economic growth in recent history. The development process is often environmentally burdensome, as countries use many fossil fuels and worryingly increase atmospheric pollution. Moreover, as these countries develop, people gradually overclass and yearn for better living conditions, but inequality is still brutal. The main developing countries are Brazil, Russia, China, India and South Africa.

a and c?

i think it is a and c

as general terms,  indian territory,  the indian territories, or  indian country  describe an evolving land area set aside by the  united states government  for the relocation of  native americans  who held  aboriginal title  to their land. in general, the tribes ceded land they occupied in exchange for  land grants  in 1803. the concept of an indian territory was an outcome of the 18th- and 19th-century policy of  indian removal. after the  civil war(1861–1865), the policy of the government was one of  assimilation.