高中第二册第四单元的单元教学重点是“按合理顺序说明事物”。《一次大型的泥石流》一文（以下简称《一次》）是凸现单元教学重点的很好的例子 ,可惜教材后的练习和与之配套的《教参》都没有对该文的顺序作实事求是的分析 ,只笼统地说主要部分采用时间顺序（《教参》观点） , The unit teaching of the fourth unit of the second volume of the senior high school is “to explain things in a reasonable order”. The article “A Large-scale Debris Flow” (hereinafter referred to as “One Time”) is a good example of highlighting the teaching focus of the unit. It is a pity that the exercises after the teaching materials and the accompanying “Guidances” did not provide a practical and realistic analysis of the order of the text. , only generally speaking that the main part is in chronological order (“instructions” view),