You are presented with the question "What can increase soil acidity?" and the following answer choices: 
- Air pollution
 - Organic compounds
 - humans disturb it
 - cactuses
 - flooding
 - deforestation
 - Pollution
 - harmful substances

Now knowing that air pollution can cause the pH of soil to decrease and acidity increases as the pH number decreases, and alkalinity increases as the pH number increases, choose the best answer.


 

 Air pollution        