Read the text and answer the question. "The future of transportation is evolving rapidly. While self-driving cars promise convenience and safety, they also raise ethical questions about decision-making in critical situations. Flying vehicles, on the other hand, offer a solution to urban congestion but face challenges regarding air traffic control and energy consumption. Despite these hurdles, engineers are optimistic about a future where travel is faster, safer, and more sustainable." What is one of the main challenges for flying vehicles mentioned in the text?
A) Lack of passenger interest