In this task, you are given a paragraph, and your job is to generate comma-separated entities present in the given paragraph. Generate entities from a given passage in such a way that (i) they are present in the paragraph, (ii) they are non-duplicate, (iii) they underwent a state change during the process. Avoid creating entities that (i) aren't present in the process paragraph and (ii) aren't significant. 

Rainwater picks up carbon dioxide from the air. Rainwater goes into soil. Water with carbon dioxide percolates through soil. The water becomes a weak acid. The water dissolves limestone. Caves form where the limestone was dissolved. 
rainwater ,carbon dioxide ,water ,weak acid ,limestone ,caves 