A noun is a person, place, or thing.
These are the sentences where the bold word is a noun:
The JUMP was his longest yet.
The soft FLOW of the river was soothing and strange.
We looked to the heavens for a SIGN.
He sustained one severe CUT after getting into an accident.
Explanation:
You can usually tell if a word is being used as a noun if a description comes after the word, like the second sentence (The soft FLOW of the river was soothing and strange.)
Also sometimes when there's an a, and, or the before a word, it means that the word is a noun, like the first and third sentence (The JUMP was his longest yet. We looked to the heavens for a SIGN.)
Sorry this took a while but I had to make sure it was explained right. Hope it helps you out :)
