Answer: the relation to, reflection of, or adaptation of cultural diversity.
The first option is the one that better defines multiculturalism. The main characteristic of multiculturalism is the importance it gives to cultural diversity. On the other hand, the second option discusses "Americanization," the third option talks about absorption into a dominant culture and the fourth one talks about the creation of marginalized groups. All of these are characteristics that multiculturalism tries to avoid.
