This year the world ’ s population ticked over to 7 billion. 21) They forecast dramatic changes unless significant steps are taken to control population growth. Here are some challenges a population of 7 billion must confront. Water is probably going to be the first real threat that we bump into. Acceess to fresh water becomes incredibly difficult. We’re seeing the impacts of overuse of water resources and that sort of pressure mounts as the world population increases. 22 ) What we’re putting into the atmosphere is going to lead to changes that haven’t been seen in millions of years. As the whole world warms up, a lot of places become very unpleasant to live in.23) We have to find less polluting sources of energy and be much more careful in the way that we make use of the remaining non-renewable fuels we’ve got. If we continue to tap the resources to meet the immediate economic demands , the supplies will run out in time. We still can’t imagine that one day we have to run the world from renewable energy resources. 24) We’ve got some major health problems with the medical services to actually attack the diseases of old age. But the real problem is that the world population is growing fastest in the developing countries. How can we cope with a double of the population when they’re already dirt poor and only just getting enough to live on? 25) Is it all doom and gloom ( 前景暗淡) as the experts suggest, or do we have a brighter future? A. Challenges range from water shortages to rising sea levels. B. Experts have painted a depressing future for life on Earth. C. All countries in the world will face the challenge of population ageing. D. Agriculture, a main consumer of water, may have to change its whole structure. E. If we hang on to them for a little bit, they’ 11 get more and more valuable in the future. F. The challenge of meeting the food needs of its ever-growing population is enormous. G. There will be much hotter temperatures, summer-time heat stress and rising sea levels.