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. 

Example Input: Rain clouds travel across the sky. Rain clouds are stopped or slowed by mountains or wind. The rain clouds drop the rain. The clouds are no longer raining when or if they reach the other side of the obstacle. On the other side of the mountains or rain, there isn't much rain. The area that receives little rain develops a very different ecosystem. The area that receives little rain becomes a desert. 
Example Output: rain clouds ,rain ,clouds ,a very different ecosystem ,desert 

Example Input: A star burns in space. Eventually it burns all its hydrogen. Becomes a red giant. Once the red giant burns itself out. The core of the star collapses. The gasses will start to disperse. Only the core is left. A white dwarf has been formed. 
Example Output: star ,hydrogen ,red giant ,white dwarf 

Example Input: Grass and small plants grow in an area. These plants die. The soil gains organic material. The soil becomes more fertile. Larger plants are able to be supported. Trees eventually grow. 
Example Output:
Grass ,Small plants ,organic material ,larger plants ,trees