The correct answer is A. Melting pot theory
Step-by-step explanation:
The Melting pot theory is a theory that applies to heterogeneous societies that have influences of different cultures during history than melt over time creating a culture that includes diverse cultural elements. Because of this, the Melting pot theory is used to describe many cultures including the one in the United States as during history the culture has been influenced by people from different cultures and backgrounds due to the high rate of immigration from the 17th century to nowadays. Thus, the theory that America is a country of different cultures fusing together is the Melting pot theory.