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. 
Q: Blood delivers oxygen in the body. Proteins and acids are broken down in the liver. The liver releases waste in the form of urea. The blood carries the urea and carbon dioxide to the kidneys. The kidneys strain the urea and salts needed from the blood. The carbon dioxide by product is transported back to the lungs. Carbon dioxide is exhaled by the lungs. 
A: 
oxygen ,proteins and acids ,waste ; urea ,carbon dioxide ,salt 