Fact 1: Air pollution can cause the pH of soil to decrease.

Fact 2: Some soils are more sensitive than others to the acid dropped by air pollution.

Given the two facts above, answer the question "some soils are more sensitive than others to a lowered what" with the following options: 
- p53
 - HPV
 - CO2
 - wolf population
 - light level
 - pH
 - sea level
 - dam


 

      pH   