What does the text suggest about hydrogen fuel-cell vehicles?

The text suggests that hydrogen fuel-cell vehicles play a significant role in promoting further research into electric vehicles. This aligns with the understanding that advancements in one technology can lead to innovations in related areas. By highlighting the potential of hydrogen fuel-cell vehicles, the text emphasizes their contribution to the broader field of sustainable transportation, encouraging innovation and exploration in electric vehicle technology. This connection indicates a positive relationship between the development of hydrogen fuel cells and the progress in electric vehicle infrastructure and practices.