There are many people in the world now. There will be even _________ people later this century. The earth will he crowded and there will be very little room _________ each person. Maybe there will be only _________ room on the earth in 600 years. That will be a very serious problem, so man is taking some _________ to solve the _________.

The moon is the satellite of the earth. Maybe man will go to live on the moon one day. _________, Americans and Chinese have _________ there. But there is no air, no plants, and no life. So _________ are doing experiments in many ways. They will find _________ to these problem __________ man can live on the moon. I’m sure our dream will come true by the end of this century.