What will the city of the future look like? No one knows for sure, and making______(predict) is a risky business. But one thing is certain-they are going to get bigger before they get smaller. In the future, care for the environment will become very important _______earth’s natural resources run out. We will use lots of_______(recycle) materials, such as plastic, steel, glass, wood and paper, and we will waste fewer natural_______.We will also have to rely more _______ alternative energy, such as solar and wind power. All this seems certain, but there are plenty of things about city life in the future _______ are not certain.