Answer: B. As more people move to China's cities, pollution has steadily increased.
Step-by-step explanation:
The key to the graph shows us that as time has gone by, the number of people moving to Chinese urban areas has steadily increased from 12.5% in 1952 to 39.1% in 2013.
In that time, pollution in the form of CO2 emissions has increased steadily as well. If one were to draw a correlational relationship from this, it would be that as more people moved to urban areas, Chinese pollution has steadily increased.