Answer : Option C) Support system.
Explanation : Support system can be the another name for Kara's sister. As when Kara started a new exercise program, Kara’s sister joined with her on a regular basis, which increased the dedication of Kara towards the physical activities and raised her confidence level too. She even talked to Kara about her progress, which motivated Kara to do better everyday.
So, support system is the best suitable name for Kara's sister.
