The best choice to connect two different regions where people are changing residence would be four: migration.
Here's a brief distinction between the options:
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Globalization: This refers to the process of increased interconnectedness and interdependence among countries, often through trade, investment, and cultural exchange. While it influences migration, it is not a direct force connecting regions in terms of people moving.
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Nutrient Pollution: This typically relates to the contamination of water bodies due to excess nutrients, primarily from agricultural runoff. It can affect local ecosystems and water quality but does not directly relate to human movement or residency changes.
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Runoff: This refers to the flow of water, usually from precipitation, that does not soak into the ground but rather flows over land and can transport pollutants. Like nutrient pollution, it pertains more to environmental impacts than to human migration or residency changes.
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Migration: This is the movement of people from one place to another, which directly involves changing residence. It is the strongest force connecting regions through the movement of populations.
Thus, migration is the force that most directly connects different regions through the changing of residence by people.