Answer: 3 Countries.
Explanation:
According to the Wikipedia website, "Three territories of EU member states have withdrawn: French Algeria (in 1962, upon independence), Greenland (in 1985, following a referendum) and Saint Barthélemy (in 2012), the latter two becoming Overseas Countries and Territories of the European Union."
C. Few valuable natural resources
Hope this helps! feel free to clarify
Effects of one migration from one population can become a cause of another migration of another population because the new population can consume the resources of the land, forcing the old population to leave in search of new resources.
