Final answer:
Joseph Bruchac learns that he is good at free throws during basketball tryouts, illustrating the importance of practice in developing skills and finding one's strengths. The correct option is C. free throws.
Step-by-step explanation:
In the context of Joseph Bruchac's experience, one of the things he discovers he is good at while trying out for the basketball team is free throws. Bruchac highlights the importance of practice and dedication, noting that through continuous effort, he was able to excel in taking free throws, which became one of his strengths on the court. This emphasizes the broader theme of self-discovery and improvement in his work.