The word in the blank should be 'segregation' :)
Europeanizationefers to a number of related phenomena and patterns of change: The process in which a notionally non-European subject (be it a culture, a language, a city or a nation) adopts a number of European features (Westernization).
I think the correct answer from the choices listed above is the third option. The barrel of a gun is also known as bore. The barrel is the metal tube which the bullet is fired and the bore is the inside of the barrel. It is the one closest to the barrel so it must be the answer.
C. Mutualistic relationship
Flowers and hummingbirds have a mutualistic relationship where both benefit. Flowers produce food in the form of nectar (sugar and water) to attract hummingbirds which, in turn, move pollen for the plant (pollination).