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Let's recap! The nominative case is the subject of the sentence. i.e. the person/thing carrying out the action (verb).
Here are some more examples: Der Mann ist sehr freundlich. (The man is very friendly) Die Schule beginnt um 8 Uhr. (School begins at 8 o'clock)
Ask yourself: Who or what is this sentence about? Whoever/Whatever is in the nominative case.