How have world economies changed during the modern era?

a. social hierarchies have disappeared as economic equality increased throughout the world.
b. economic philosophies such as capitalism and communism have been developed.
c. countries have become more economically isolated from one another.
d. environmental protection has become more important than economic growth.

Option B.

Explanation:

Economic philosophies such as capitalism and communism have been developed, is the right answer.

The economy of the humans of the world is known as the world economy. It is regarded as the world economy because of the global exchange of goods and services that are displayed in financial units of description. "World Economy" is just a gross of the different nations' measurements.

to act quickly in times of danger to the united states

because you have to act quickly if you want to live/survive.