A、To grow green, healthy and high yielding crops. B、To save energy resources that will be largely consumed by 2030. C、To protect

Speaking at the Sustainable Development conference in London, Britain’s chief scientific advisor warns that under the backdrop of a growing global population, the world will face a "perfect storm" of threats as food, water and energy shortages combine to impact society by the year 2030. Dr. John Beddington says in just more than 20 years, the world’s population will reach 8.3 billion. In and of itself, that means needs will be greater in the future. As this happens, Britain’s chief scientific advisor warns that resources will be under increased pressure and climate change will also come into play, exacerbating problems. "There is an increase in the demand for food. That is going to be up by about 50 percent by 2030," Dr. Beddington said. "The increase in demand for energy is going to be up by a similar amount and the demand for fresh water, which is really very important, is going to be up by something like 30 or 40 percent."
    Professor Beddington says now that oil prices have dropped again, domestic and international pressure to deal with energy issues that we will have to confront in the future may well decline. But he underlines it is absolutely necessary to develop green solutions to lessen the impact that climate change will inevitably bring. The U.N. Environment Program predicts the amount of fresh water available will drop off sharply in parts of Africa, Asia and Europe by the year 2025. If little is done in the coming years, Beddington says the "perfect storm" of threats will increase the likelihood of unrest, conflict and mass migration in various parts of the world.
Questions 19 to 21 are based on the passage you have just heard.
19. What is the passage mainly about?
20. What will the world’s population be in about 10 years, according to Dr. John Beddington?
21. Why does Professor Beddington suggest developing green solutions?