instruction:
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. 
question:
There is a fetus in the womb. They are born and are a baby. The baby grows into a child. Puberty turns the child into an adolescent. The adolescent becomes an adult. An adult becomes an elderly person. The elderly person dies. 
answer:
fetus ,baby ,child ,adolescent ,adult ,elderly person 


question:
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. 
answer:
bark ,ring 


question:
You breathe in through your nose or mouth. The air travels through your windpipe. Into your lungs. Inside your lungs are tiny air sacs. The air sacs transfer the oxygen into your blood. The oxygen travels through your blood stream. The carbon dioxide from your blood stream is transferred to your air sacs. You breathe out and expel the carbon dioxide from your lungs. 
answer:

air ,oxygen ,carbon dioxide