You are presented with the question "some soils are more sensitive than others to a lowered what" and the following answer choices: 
- p53
 - HPV
 - CO2
 - wolf population
 - light level
 - pH
 - sea level
 - dam

Now knowing that air pollution can cause the pH of soil to decrease and some soils are more sensitive than others to the acid dropped by air pollution, choose the best answer.


 

      pH   