When a boy becomes a teenager, he often wants to show his independence.

http://grammar.ccc.commnet.edu/grammar/pronouns1.htm

Scroll down to Personal Pronouns and see what you think. Then, once you've identified the TWO instances of personal pronouns in this sentence, you'll need to decide which noun the pronouns are referring to.

Let us know what you think, and someone here will give you feedback.

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In the sentence "When a boy becomes a teenager, he often wants to show his independence," the personal pronoun is "he," and its antecedent is "a boy."