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In 1900 there were 1.6 bilion people in the world, but today that number is over 6 bilion. In the last century, a lot of the world's forests 1. _____ (destroy) to provide wood for making furniture and paper. In addition, many of the world's seans and rivers 2. ______ (pollute).
Another problem today is how to provide food for the growing number of people in the world. New ways of growing food 3. _______ (need) very soon. Some new foods 4. _______ (discover) by scientics in the last few, and in the future we will eat more of these.
Living space will be another big problem in the future. Perhaps one day new cities 5. _____ (not build) on land any more - we build them on or under the sea! ​