You are presented with the question "What is common in the southwestern portion of the subsection?" and the following answer choices: 
- permineralization
 - deuterostomes
 - barrel-shaped
 - cactuses
 - swamp vegetation
 - peachleaf willow
 - precipitation
 - gene flow

Now knowing that sinkholes are formed by precipitation and sinkholes are common in the southwestern portion of the subsection, choose the best answer.


 

       precipitation  