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.

d. it adversely affected american productivity

i just did something on this guy a few days a go give me two minutes to find it in my notes.