The tendency to assume that one's culture and way of life are superior to all others is termed
a. cultural relativism.
b. ethnocentrism.
c. prejudice.
d. assimilation.

Hm, I think the question here calls for "d", although d would be better defined as a focus on one's own culture, and ignoring other cultures, or seeing other cultures through the lense of own culture.

In a way, prejudice could be a good lead, but only if it said "prejudice towards all other cultures" which is not really feasible (one can't know all other cultures).

so, still, d is best, although there can be ethnocentrism without feeling superior

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