What is one of the defining characteristics of the modern era? A-Countries are better able to build strong economies without trading with their neighbors.
B-Most countries have done away with social and economic hierarchies.
C-Human actions have less of an impact on the environment than they did during other eras.
D-Interactions and exchange between cultures have become easier than ever before.

D - Interactions and exchange between cultures have become easier than ever before.

Explanation:

Though this question may seem tough at first, we can easily find the answer through the process of deductive reasoning.

The first choice, A - "Countries are better able to build strong economies without trading with their neighbors." is clearly incorrect due to the increased prevalence of interconnected, truly globalized trade throughout the modern era. Not to mention that most stable, prosperous economies throughout this era were built off of foreign imports from neighboring regions.

The second choice, B - "Most countries have done away with social and economic hierarchies." is also incorrect, due to many civilizations maintaining political order through such hierarchies. This is seen in enduring policies such as the Indian caste system, or the feudal system of Japan at the time.

The third choice, C - "Human actions have less of an impact on the environment than they did during other eras." is the most absurd one yet, mostly due to its nonsensical outlook. As humans progress throughout history, environmental degradation constantly increases, especially seen in things like the creation and use of gunpowder, or new agricultural technologies.

The fourth choice, D - "Interactions and exchange between cultures have become easier than ever before." makes the most logical sense here, due to the cultural diffusion; maritime, interconnected trade; and spread of various religious and traditional aspects at the time.  

By avoiding close interaction with other nations