In what part of china did the population decrease the most? in the northeast in the northwest in the southeast in the southwest

In the northwest of China the population decreases the most. Option B is correct.

The northwestern part of China is one of the most inhospitable places for living in the country since it is characterized by extreme temperatures, presence of desert as well as dry steppes.

Northwestern China includes the autonomous regions of Xinjiang and Ningxia and the provinces of Shaanxi, Gansu, and Qinghai.

its c

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.