Complex sentence: By hearing inspiring stories, Nakamura pondered why people would try to help someone they had never met; he considers this question and the necessity to act to build a better future to be the main themes of "C".
Split into simpler sentences: By hearing inspiring stories, Nakamura pondered why people would try to help someone they never met. This question and the necessity to act to build a better future are considered by Nakamaura to be the main themes of "C".