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: The bat sends out sound waves from their mouth or nose. The sound waves hit an object. Echoes are produced. The echo returns to the bat's ears. The bat hears the echo. The bat can figure out where the object is located. 
Example Output: sound waves ,echo 

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: Acid rain makes waters acidic. Causes them to absorb aluminum from soil. The water runs off from the soil into lakes, streams, etc. Fish and their eggs die. Frogs and plants die. Insects and other wildlife die. The ecosystem is out of balance, causing further problems. 
Example Output:
water ; acidic water ,aluminum ,fish and their eggs ,frogs and plants ,insects and other wildlife