R: How do you know that Najiah Knight is serious about her sport?
A: Najiah Knight is serious about her sport because she dedicates herself to rigorous training and workouts.
C: The text states, "She trains hard... Najiah works out every day. She does exercises that build her muscles." This shows her commitment and determination to improve her skills in bull riding.
By putting in this effort and aiming for the top rank, Najiah demonstrates her seriousness about becoming the best bull rider.