Refer to the map below to answer the following question: A map image of ancient China is shown. The region is divided into sections. The map shows the population change over a period of time in China. In the northeast, the population has decreased. In the northwest, the population has increased slightly or remained the same. In central and south China, the population has increased considerably. In the southeast, the population reached the highest level of increase.

In what part of China did the population decrease the most?

in the northeast
in the northwest
in the southeast
in the southwest