Final answer:
The dividing line between Humid and Arid China is marked by the extent of the Mongolian steppe.
Step-by-step explanation:
The dividing line between Humid and Arid China is roughly marked by the extent of the Mongolian steppe. The vast arid regions of western China extend into the Gobi Desert between Mongolia and China, while the northern and eastern parts of China are characterized by more humid climates. The Mongolian steppe, located north of the Great Wall and encompassing the autonomous region of Inner Mongolia, consists of broad flat grasslands that extend north into the highlands.