Plagiarism - posting the work of others with no indication that it is not your own - is frowned on by our community, and may result in your answer being down-voted or deleted.
When you find a useful resource that can help answer a question (from another site or in an answer on MathOverflow) make sure you do all of the following:
- Provide a link to the original page or answer
- Quote only the relevant portion
- Provide the name of the original author
According to Ernest Hemingway - Biographical on Nobelprize.org, Hemingway saw combat when he was a teenager. It says:
After the United States entered the First World War, he joined a volunteer ambulance unit in the Italian army. Serving at the front, he was wounded, was decorated by the Italian Government, and spent considerable time in hospitals ....
[other sources, quotes, explanations, etc. necessary to complete the answer]
Do not copy the complete text of external sources; instead, use their words and ideas to support your own. And always give proper credit to the author and site where you found the text, including a direct link to it.