The sentence that proves Nina is having to adjust to a new place as she is about to begin college is:
C. "As her uncle lifted them off the ground, Nina felt the plane detach from the water, but she knew she was leaving behind more than mere earth" (paragraph 7).
This sentence indicates that Nina is physically leaving her familiar surroundings and implies a sense of emotional transition and adjustment to a new life and environment as she embarks on her journey to college.