The answer is D. They were strong communicators
C. was passed to keep America ethnically uniform.
Answer:
Isolationism was stronger after the depression
Explanation:
After WWI, USA became more active economically and military in aid for Europe's countries in post-war recovery. This meant that many European countries depended on US loans to recover. After the crash in 1929, USA became more conscious about their own economy and stopped participating in European conflicts. This encouraged countries such as Germany or Japan to take action in order to expand territory, which gave place to the raise of fascism in these countries (Japan's INnvasion of China in 1937 and Germany's annexation of Czechoslovakia in 1938, for example)
I believe the answer is: positive externality
Positive externality refers to The benefit that enjoyed by a third party when the first and second party are conducting a transaction.
When you receive a vaccines, you prevent yourself from becoming a host that could contaminate other people from getting the virus. In the example above, you and your children are the first and second party. And other children are the third party.