Fact 1: Sinkholes are formed by precipitation.

Fact 2: Sinkholes are common in the southwestern portion of the subsection.

Given the two facts above, answer the question "What is common in the southwestern portion of the subsection?" with the following options: 
- permineralization
 - deuterostomes
 - barrel-shaped
 - cactuses
 - swamp vegetation
 - peachleaf willow
 - precipitation
 - gene flow


 

       precipitation  