The true statement about immigrants is:
Immigrants are people who seek to live in other countries for good.
The other statements are not accurate. Immigrants are not limited to those who go to America, and "immigrant" specifically refers to people, not animals or objects. The "melting pot" concept relates to the idea of different cultures assimilating into a single culture, often in the context of the United States, but it does not solely reference all immigrants seeking to come to America.