爱华网extent是个名词，意为“程度；范围；长度”。
eg: The Internet is justlike a double-edged sword. Whether it does good or harm to usdepends, to a great extent, on how we exploit and useit.互联网就像一把双刃剑。它对我们有益还是有害在很大程度上取决于我们如何开发利用它。
extend和expand都是动词，extend本意为stretchout,它侧重是二维的平面的延伸。而expand可以指三维意义上的膨胀，与contract ‘收缩’相对。
extend是指延伸，extend:make sth.longer / larger / wider in time,space,area.
eg: We have the desire to knowmore things about this world and is can extend our visual field.我们想了解更多有关于这个世界的东西并拓宽自己的视野。
expand含有膨胀的意思，人口激增就用expansion 。expand: become greater in size,number or importance
eg: The big western oilcompanies are trying to expand through acquisitions and investment,but the opportunities do so are becoming scarcer.西方的石油大公司在尝试通过并购和投资来扩张,不过这样的机会已经越来越少。
