Sagan believes that before the earth's resources are completely exhausted it will be possible to change the atmosphere of Venus and so create a new world almost as large as the earth itself. The difficult is that Venus is much hotter than the earth and there is only a tiny amount of water there.

　　Sagan proposes that algae organisms(海藻有机体) that can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in condition similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceship will then fly to Venus and fire the rockets into the atmosphere .In a fairly short time, the algae will break down the carbon dioxide into oxygen and carbon.

　　When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for man to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.

　　32.In the long run, the most difficult problem caused by population growth on the earth will probably be the lack of ______.

　　A. oil

　　B. food

　　C. resources

　　D. space　

　　33.Carl Sagan believes that Venus might be a living place because _____

　　A. the days on Venus are long enough

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