Policeman catches thief.
Meaning: This means a person whose job is to enforce the law and protect people is seizing or capturing a person who steals something.
Choice of Words: Policeman is a person whose job is to enforce the law and protect people. Catches is the third person singular present tense form of the verb "catch", which means to seize or capture someone or something. Thief is a person who steals something, especially secretly or without permission.
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