Read the text below. For questions 47 to 51, choose the best answer (a, b, c or d).
‘Heavier than air flying machines are impossible,’ said the well-known scientist Lord Kelvin in 1895. Thomas Watson, the chairman of IBM in 1943, was wrong too when he said that he thought there would be a world market for only five or so computers.
Predictions can, of course, be wrong, and it is very difficult to predict what the world will be like in 100, 50, or even 20 years from now. But this is something that scientists and politicians often do. They do so because they invent things and make decisions that shape the future of the world that we live in.
In the past they didn’t have to think too much about the impact that their decisions had on the natural world. But that is now changing. An increasing number of people believe that we should live within the rules set by nature. In other words, they think that in a world of fixed and limited resources, what is used today will not be there for our children. We must therefore look at each human activity and try to change it or create alternatives if it is not sustainable. The rules for this are set by nature, not by man.