听力原文：We've been living through times of plenty in recent decades, but no more. World grain sup- plies are low, there's just forty days' worth in stock and the long-term future looks bleak. Our demand for foods predicted to rise 50% by 2030. The statistics are startling. The world's population is set to explode from over 6 billion now to 9 billion by 2050. The increase is mainly in the developing world. In countries like China and India, an economic boom is increasing their wealth and dramatically altering the traditional diet. New western habits are taking hold, the McDonald's wave becoming a familiar sight in unexpected places. More meat and dairy products require more land and water. All the ingredients are there for a future food crisis. And it's the first priority of the UK's new chief science adviser. Which of the following statements is closest in meaning to the passage you have just heard?