Instructions: 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. 
Input: The growing season starts. Bark grows on a tree. The inside of the tree grows. The bark is pushed out around the tree trunk. The bark leaves a ring. The growing season slows down and ends. 
Output:
bark ,ring 