What is the simplest way to understand population change?

Correct answer: Seeing how many people were added and reduced

Direct answer: Option A. The simplest method is to count what adds people and what removes people. Births and in-migration add people to a place. Deaths and out-migration reduce its population. In a basic expression, population change depends on natural change plus migration balance: births minus deaths, together with in-migration minus out-migration. No difficult calculation is needed for this question; first identify increases and decreases. Option A is correct because it describes this addition-and-reduction method. Option B is wrong because the name of a river does not measure population change. Option C is wrong because mountain height may affect settlement, but it is not a direct population-change process. Option D is wrong because weather colour is not a demographic measure and cannot show how many people entered or left. Memory cue: ask two questions—who came or was born, and who left or died?