Answer: appendix is my guess
Explanation:
serves as a source of neural stem cells (NSCs) in the process of adult neurogenesis.
The best answer to fill in the blank would be ''Bystander'' because as that role you can go tell any adult or higher authority to stop the fighting so you don't try to be a hero and get yourself hurt as well.
True. Social is different from happiness or sadness.
ANWSER .08% Hope this helps