Speaking and writing are different in many ways. Speech depends on sounds; writing, on the other hand, uses written symbols. Speech was developed about 500 000 years ago, but written language is a recent development, invented only about six thousand years ago. Speech is usually informal, while the word choice of writing, by contrast, is often relatively formal. Although pronunciation and accent often tell where the speaker is from, they are ignored in wiring because a standard diction and spelling system prevails in most countries. Speech relies on gesture, loudness, and the rise and fall of the voice, but writing lacks these features. Careful speakers and writers are aware of the differences．
4． 有损连贯性的几种情况：
　　考生在写作中经常出现下面几种错误：

　　1）不必要的改变时态，比如：
　　In the movie, Robert Redford was a spy. He goes to his office where he found everybody dead. Other spies wanted to kill him, so he takes refuge with Julie Christie. At her house, he had waited for the heat to die down, but they come after him anyway.
　　2）不必要的改变单复数，比如：
　　Everybody looks for satisfaction in his life. They want to be happy. But if he seeks only pleasure in the short run, the person will soon run out of pleasure and life will catch up to him. They need to pursue the deeper pleasure of satisfaction in work and in relationships.
　　3）不必要的改变人称，比如：
　　Now more than ever, parents need to be in touch with their children's activities because modern life has the tendency to cause cleavages in the family. You need to arrange family like
it so that family members will do things together and know one another. You need to give up isolated pleasures of your own and realize that parents have a set of obligations to sponsor togetherness and therefore sponsor knowledge.

　　因此写作中，一定要注意时态，人称以及数的变化是否正确，要注意保持一致。