Final answer:
Kirk shows care for his sister by expressing his willingness to take her to school once he has a car, as stated in option D.
Step-by-step explanation:
The sentence from the story that implies Kirk cares about his sister is option D: "When I have a car, I can take you to school." This sentence suggests that Kirk is thinking about his sister's needs and is willing to help her by providing transportation to school once he has a car. It showcases a sense of responsibility and consideration, which are indicative of care and affection.