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. 

Solution caves are formed in limestone and similar rocks by the action of water. After a rain, water seeps into cracks and pores of soil and rock. The water percolates beneath the land surface. Some of the water reaches a zone where all the cracks and pores in the rock are already filled with water. Rainwater absorbs some carbon dioxide as it passes through the atmosphere and even more as it drains through soil and decaying vegetation. The water combines chemically with the carbon dioxide. A weak carbonic acid solution is formed. This acid slowly dissolves calcite, forms solution cavities, and excavates passageways. 
Solution caves ,carbon dioxide ,weak carbonic acid solution ,calcite ,solution cavities 

Trash is put into a household trashbag. The trashbags are thrown into a large outdoor trashcan. The trashcan is emptied by a large trash truck. The trash truck travels to the landfill. Unloads all the trash the truck has collected. 
trash ,trash truck ,trashbags 

An egg is laid by a mother bird. A baby bird forms within the egg if it is fertilized. The baby bird begins pecking out of the egg. The baby bird is unable to fly to get food. The mother bird must feed the baby bird food. The bird grows stronger and grows wings. The bird is able to fly. The bird is able to leave the nest and find food. The bird is able to reproduce. 

egg ,baby bird; bird ,wings