Answer: D. The author uses his or her own friends as examples.
Explanation: The author makes the point: "They learn that they are good at something and feel proud of that."
Then, the author goes on afterwards saying, "For example, my classmate Elizabeth has played basketball for three years. When she first started, she barely knew how to dribble. Now, she makes two out of three free throw shots."
^^ The author is supporting their point with the evidence of his or her own friends as examples.