75% species go extinct to be considered a mass extinction
Answer;
Acid rain is mostly a problem in the Northern Hemisphere.
Explanation;
This can be attributed to the fact that the area has a large, densely populated cities and a concentrated number of industrial and power plants in an area. These factors contribute to acidic gases in the environment such as sulfur oxide, nitrous oxide, which mix with rain water to form acidic rain. Additionally, prevailing wind direction which brings with it the pollution from the midwest to the north east.
To awnser your question, I would say C.