In the context of Central Place Theory, high-order goods are those that are more expensive, less frequently purchased, and typically require a larger market area to be viable. These goods usually have fewer sellers compared to low-order goods.
Among the options provided, a refrigerator (Option D) is a high-order good. It is a more expensive item that people do not buy frequently and typically requires consumers to travel further to purchase it compared to low-order goods like milk or bread.
Therefore, the answer is:
D a refrigerator