A. Automobile exhaust
B. Forest fire
C. Bacterial action in soil and swamp areas
D. All A., B. and C.
Correct Answer: Automobile exhaust ✔
Last Updated: March 11, 2019
A. Automobile exhaust
B. Forest fire
C. Bacterial action in soil and swamp areas
D. All A., B. and C.
Correct Answer: Automobile exhaust ✔
Last Updated: March 11, 2019