范文：
　　Nowadays humanity is faced with a lot of troublesome problems: energy crisis, cancer, pollution, population explosion, tec. They are threatening the survival of humanity. Therefore, some people are pessimistic about the future of humanity.
　　They are pessimistic because they think that limited energy on earth will be exhausted soon; incurable diseases are threatening more people's lives; pollution is worsening the environment; population explosion will make food shortage even more serious.
　　Actually they needn't worry too much about these problems. Scientists will have developed new energy resources by the time oil and coal are used up. Besides, scientists are making a thorough study of genes and they will manage to cure cancer by adjusting the arrangement of genes. They are also making efforts to control pollution and population. Furthermore, all the governments in the world are concerned about these problems and they ahve taken measures to solve these problems.
　　Therefore, we have every reason to be sure that human beings will conquer nature but they will never be conquered.