I need the entire sentence for context before I can answer the question. All of these options could be a subject, but you need to give context.
Answer:
Yellow fever is a disease caused by a virus that is spread through mosquito bites. Symptoms take 3–6 days to develop and include fever, chills, headache, backache, and muscle aches. About 15% of people who get yellow fever develop serious illness that can lead to bleeding, shock, organ failure, and sometimes death.
Explanation:
I copy and pasted this from the internet but you can easily summarize this in different words.
