Option D is the correct answer because “outskirts” means the outer part of a town or a city, hence it is correct.
Option A is incorrect because “rim” means the outer edge of an object, usually circular objects, hence is incorrect .
Option B is incorrect because “core” mean self the most central and important part of an object in the centre, which is incorrect because it can only exist in substances.
Option C is incorrect because “periphery” means the exact border or outline. While outskirts means the part of the twin near the border hence it is incorrect.