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情态动词是助动词的一种，一些可以表示可能性，一些可以用于提建议。不管是表示可能性还是用于提建议，这些情态动词有的具备确定性，有的不具备确定性。
情态动词will常用于表达确定（certain）的想法或情况。
□ Tropical logging in developing countries brings many long-term environmental risks. If logging is uncontrolled, deforestation, soil erosion and even climatic changes will occur. Until the governments realise the important role forests play in maintaining our natural environment, they will continue to exploit and destroy these forests.
发展中国家的热带采伐带来了许多长期的环境风险。如果伐木不受控制，森林破坏、水土流失甚至气候变化都将会发生。在各国政府认识到森林在保护我们的自然环境中所起的重要作用之前，它们将继续开发和破坏这些森林。
注意：情态动词can也可以表达确定的观点和情况，但是不如will语气强烈（less certain）。
□ One advantage of worldwide media is that films, plays, music and sports events can be enjoyed and celebrated around the world. Many people believe that sharing these aspects will create a global culture that brings people closer together.
世界媒体的一个优势是电影、戏剧、音乐和体育活动可以在世界各地欣赏和庆祝。许多人认为，分享这些方面将创造一种全球文化，使人们更加紧密地联系在一起。
□ The international media has provided a valuable educational tool for children and adults alike. Foreign television teams keep the public up-to-date with news and images of different cultures and ways of life. Thus, people can educate themselves about these cultures not just by reading books but by watching news programmes and documentaries. In this way, global culture will bring valuable educational benefits worldwide.
国际媒体为儿童和成人同样提供了宝贵的教育工具。外国电视团队不断向公众提供不同文化和生活方式的最新的新闻和图像。因此，人们不仅可以通过阅读书籍，还可以通过观看新闻节目和纪录片来了解这些文化。这样，全球文化将给全世界带来宝贵的教育利益。
情态动词can，could，may，might通常用于表达观点的不确定性（tentative）。
□ However, it is important that the disadvantages of tourism are not overlooked. A foreign tourist, who has become infected with a disease, could start an epidemic when they return home or travel to other countries. The HIV virus is one example of diseases that has now become a worldwide epidemic.
然而，旅游业的弊端不容忽视，这是很重要的。感染了疾病的外国游客回国或前往其他国家旅行时，可能会引发流行病。HIV病毒是现在已经成为世界性的流行病的一个例子。
雅思Task 2题目有时候会要求写作与未来有关，这时候，可以用情态动词may，might，could，would表示不确定性（tentative）。
□ There are also some advantages to cloning. Many couples are desperate to have children but are unable to have children naturally. Cloning may solve this problem. Cloning could also be used to create spare organs for surgery. Therefore, if you needed a heart transplant, you could be given a spare heart which has been cloned in an organ bank.
克隆也有一些好处。很多夫妻都渴望有孩子，却不能自然地有孩子。克隆技术可以解决这个问题。克隆技术也可以用来制造手术所需的备用器官。因此，如果你需要心脏移植，你可以得到一颗在器官库里克隆出来的备用心脏。
情态动词might，could和would也经常用在if从句的主句中，表达对未来的不确定（tentative）。
□ If scientists spent more time studying new species of rainforest plants, they might find a cure for cancer.
如果科学家花更多的时间研究新的热带雨林植物物种，他们可能会找到治愈癌症的方法。
□ If people lived for two hundred years, their body organs would start to deteriorate.
如果人活200年，他们的身体器官就会开始衰退。
注意：在这两个if从句中，谓语动词分别是spent和lived，主句使用might和would表示“与现在或将来事实相反”，主句和从句的动作都是不可能做到的事情。
如果主句和从句表达的内容都可能发生，主句就可以用will表示对未来的确定，从句使用一般现在时态。
□ If governments cannot control logging, the result will be deforestation, soil erosion and even climatic changes.
如果政府不能控制伐木，后果将是滥伐森林、土壤侵蚀甚至气候变化。
如果是对过去事实的假设，即“与过去事实相反”，则可以使用“If sb. had done sth., sb. would/ could/might have done”的结构。
□ If measures had been taken earlier, the rate of juvenile delinquency would have decreased.
如果早点采取措施的话，青少年犯罪率就已经降低了。
有些句子不含条件从句，而是用介词或介词短语表示假设。
□ Without the natural talent, continuous training would be neither attractive nor productive, and without the training, the child would not learn how to exploit and develop their talent.
如果没有天赋，持续的训练可能既乏味又无效；如果没有训练，孩子就不会学习到如何开发和发展他们的天分。
当然，可能性还可以用其他的结构表示，如“may well”“might just”“be (very/less/more) likely to do”“it is highly likely that”“it is quite possible that”“in a probability”。
□ On a global scale, AIDS may well become the leading cause of infant death.
在全球范围内，艾滋病很可能成为婴儿死亡的主要原因。
情态动词must用于提出一些强烈的建议。
□ Encouraging people to save energy is only a very small step towards saving our resources. In the long term the government must find alternative sources of power.
鼓励人们节约能源只是我们迈向节约资源的一小步。从长远来看，政府必须找到可替代的能源。
情态动词could，ought to，should常用于提出一些不确定的意见，不确定的程度是could＜should ＝ought to。
□ One of the major problems today is that natural resources such as coal and oil are not renewable and are sunning out extremely quickly. It is therefore important to reduce the quantity of natural resources used. To be more economical, for example, the government should encourage people to drive smaller cars, and cars could be adapted to use petrol more efficiently. Moreover, people should use public transport whenever possible. This could be done by taxing cars heavily and using this money to improve the quality of public transport.
如今的主要问题之一是像煤和石油这样的自然资源是不可再生的，而且正在以极快的速度消失。因此，减少可使用的自然资源的数量很重要。例如，从更经济实惠的角度，政府应该鼓励人们驾驶小型汽车，汽车可以被改造以更有效地使用汽油。此外，人们应该尽可能使用公共交通工具。这可以通过对汽车征收重税以及使用这笔钱来提高公共交通的质量来实现。