Answer: c. i., ii., and iii. only.
Explanation:
The Chinese government towards the last years of the 20th century and proceeding into the 21st, engaged in massive programs to plant large amounts of trees in northern China.
One purpose of this was to stop the erosion that had become rampant in the area by having the trees act as windbreakers and soil anchors. The trees were also meant to improve air quality as they would provide the air with more oxygen and take in carbon dioxide.
