The correct sequence of the regions in terms of the descending order of their population is option 4, which is I, III, and II.

Option 1 is incorrect because it lists Europe (I) as the most populous region, followed by Latin America and the Caribbean (II), and then North America (III), which is incorrect.

Option 2 is also incorrect because it lists Latin America and the Caribbean (II) as the most populous region, followed by Europe (I), and then North America (III), which is also incorrect.

Option 3 is incorrect because it lists North America (III) as the most populous region, followed by Latin America and the Caribbean (II), and then Europe (I), which is incorrect.

Therefore, the correct answer is option 4, which correctly lists Europe (I) as the most populous region, followed by North America (III), and then Latin America and the Caribbean (II).