In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: Some people are pessimistic when they think about the future. They say that a hundred years from now, we will have used most of the earth's resources. We will have polluted our seas badly, and be unable to eat fish from them. We will have made the air so dirty that we will need to wear masks. The world's population will have doubled, and we will have used all the countryside for housing; there will be no farmland left. Other people believe that Man adapts very easily. They have a different idea of the future. How, in their views, will people be living in a hundred years' time? One architect believes that Man will move off the land. He suggests that the city of the future will be a huge, pyramid-shaped building, which will be floating on the surface of the sea. About 5,000 families will be living there, and the building will contain shops and schools as well as homes. By living on the sea, we will give the farmers more land to grow crops. As for oil, people will no longer need it: we will be heating our homes with power from the sun. And we will not be short of minerals, because there are plenty under our oceans. At the moment, we do not have the technology to get them out. But, in a hundred years' time, the optimists say, the new sea cities will be using these resources. What will be in the shops in the year 3000? What will people be wearing? How will people be traveling? Scientists who make predictions about the future suggest that, by the year 3000, shops will no longer exist. Computers will have replaced them, and people will order goods from home. People will be wearing very light, thin clothes. By this time, scientists will have invented a fabric that keeps us cool in hot weather and warm in cold weather. As for travel, the experts say that most people will be using public transport. Electric cars will be traveling through the streets day and night. Anybody will be able to stop one and use it. An interesting picture. Unfortunately, we will not be there to see if these predictions come true.
Answer: we'll have polluted the air so badly that it'll be impossible for us to breathe without masks.
Pessimists believe that in the future _ .