Final answer:
The statement exemplifies the theme of human-environment interaction in geography, as the Chinese planted barrier tree lines to slow the expansion of the Gobi desert.
Step-by-step explanation:
The theme of geography that is best exemplified by the statement is human-environment interaction. Human-environment interaction focuses on how human beings interact with their environment and how they modify it to meet their needs. In this case, the Chinese planting barrier tree lines along the edge of the Gobi desert to slow its expansion demonstrates how humans are modifying the environment to prevent desertification.
Learn more about human-environment interaction