Biofuel enthusiasts, including the new US president, say food crops can provide a cleaner, greener source of energy than fossil fuels. Yang Fangyi urges caution.

• 包括美国新总统在内的生物燃料热衷者称，与化石燃料相比，粮食作物能够提供更加清洁、绿色的能源。杨方义呼吁需谨慎对待。