Which example shows physical and human factors together increasing population density?

Correct answer: Irrigation roads and markets developing in a fertile plain

Direct answer: Option A is correct. Physical factors come from nature, while human factors are created or developed by people. A fertile plain is a physical advantage because its soil is suitable for farming. Irrigation supplies water, and roads and markets support transport, trade and employment; these are human or economic advantages. Together they attract people and can increase population density. Option B describes an empty snowy area and lack of transport, both discouraging settlement. Option C gives water scarcity in a desert, which makes dense settlement difficult. Option D gives steep slopes and limited farming, also discouraging large settlements. Memory cue: fertile land plus facilities usually attracts people.