That would be the nervous system.
Answer:
You didn't seem to add who Alison is, but the answers give me enough to say which answer is correct.
Of course, there is a very large difference between feeling down and having a serious problem.
Not wanting to go back to school after summer break is completely natural and makes sense, it is just feeling down.
Feeling different from your friends is an issue that people often say isn't that bad, but it is, though rarely requires medical help.
Hearing voices is something that does require medical/professional help. This has a very high chance of being due to schizophrenia, bipolar disorder, and sometimes things such as lack of sleep, drug use, or extreme hunger. Hearing voices is the answer. These issues are serious mental health issues that will definitely need professional help.
An author's credentials can determine a health source's credibility. None of the other options would apply to credibility. When it comes to health, if you want to make sure that what you are researching or reading is authentic and reliable you need to find out whether the author is a professional health expert or not. You can do this by finding out their credentials.
Answer: You could offer to volunteer at a Hospital, or you could help teach others about their health and wellness, and also help with donations towards Hospitals and Clinics.
Hope this helped!