Answer:
American physician and medical researcher who developed the first safe and effective vaccine for polio.
Explanation:
Base on my research, during the 1800s the imperialist built military bases around the world to protect their territory and industry. And also during this period, the imperialist prefer to take over undeveloped countries to expand their empires where these countries are abundant in natural resources.
B. The chemical nature of the substance does not change
The study and practice of international relations in today's world is valuable for many reasons: ... International relations allows nations to cooperate with one another, pool resources, and share information as a way to face global issues that go beyond any particular country or region.